The Summa Theologica of St Thomas Aquinas
Christian Wisdom explained philosophically.

James F. Ross

Text of August 26,2001 Copyright James Ross 2001

This is a draft and none of it may be reproduced or quoted without permission.

10/3/2001 7:30 PM

Introduction. This is more than a philosophical work. It is a systematic exposition of a whole Christian conception of the world within philosophical principles and concepts.

The work is clear, compressed, and explicitly reasoned, with vivid examples. It is arranged into questions, answers, objections and replies. Its structure, nevertheless, seems complex, like cathedral architecture; the analytic tables in most English editions help one locate and see the order of issues. The organization is not according to philosophical priorities, but, rather, theological ones, so there is not a formal rationale and defense of its underlying philosophical skeleton. The scholarly reader has to extract that, supplementing it from Aquinas’s other works. This book explicitly addresses the vast Western literature from ancient times. It still stands, nearly 800 years later, as the single most comprehensive exposition of the whole of Latin Christian wisdom. Because of the book’s massive scope and detail, this survey has to be restricted to some major topics.

Some facts. The Summa (the conventional short name for the book) is in three parts, the second divided into two parts, with 512 Questions, 2,669 Articles, and about 10,000 objections and replies, overall about 1.8 million words, nowadays in nearly 3000 double-columned pages. It was written in about five years, along with major commentaries on Aristotle and on Scripture. It is usually reprinted now in English translation, in 5 paperback volumes.(See bibliography; and is on the “Web” in English at ).

References to the Summa are made by numbered Part, Question, Article, and Reply to Objection. The name of the book is often left out or abbreviated as “S.T”.; and it is typically cited like this, say: “I, 21,3, ad 4”, to read “Part I, Question 21, Article 3, “reply to objection 4” (the Latin ad means “to”). The questions on a single major topic are grouped by editors into “Treatises”; for instance, “The Treatise on God” (I, 1-26), “The Treatise on the Trinity”(I, 27-43), “The Treatise on Man”, (I, 75-102), “The Treatise on Law”(I-II, 90-108.

It has the three main parts. Part I: The Being and Nature of God, including the Trinity of Divine Persons, the creation of the cosmos, the origins of good and evil, and the creation and nature of angels and of man, and, finally, the divine governance of the world, about 600 pages, in 119 questions.

Part II has two sub-parts: I-II (“the First Part of the Second Part”) treats human happiness and fulfillment and the means to it, the nature and components of human acts, particularly, freedom and the voluntary, the passions, emotions, feelings and habits, and the principles regulating human actions: (i) internally, namely, the virtues and vices; and, (ii) externally, law and divine grace, about 500 pages. Included there is the vastly influential Treatise on Law, I-II, 90-108, which contains the foundation for moral law, and then for civil law, the limits on government power, and the rights of revolution, civil disobedience and just war, and a commentary on ancient Biblical (Talmudic) law and its relationship to the New Testament. It concludes with six Questions on divine grace.

Part II-II ( “the Second Part of the Second Part”), is a full-scale, applied moral philosophy, organized under the theological virtues of Faith, Hope and Charity (love), and the natural virtues of prudence, justice, temperance and fortitude, exploring the vices opposed to each by excess and deficit, and their sub-divisions, along with four Questions (II-II, 67-71), on the obligations of judges, attorneys, witnesses and defendants in legal actions. The classification and rationales for the virtues and vices are extensive, learned in ancient and Roman thought, and have had immense influence, notably, upon Dante’s Comedia, and on Milton, Chaucer and Shakespeare and the rest of Western and Russian literature and art.

Part III is almost exclusively concerned with the supernatural events about Jesus: the Incarnation, Redemption, Resurrection, and the Sacramental aids to individual humans, though it is expressed and explained in the philosophical categories and principles that thread throughout the whole book, sometimes expanded for the context, for instance, the distinctions in the notions of ‘necessity’ found in III, 46,1. Thomas died at age 49, before finishing the treatment of Sacraments, so the rest of his plan for Part III, covering the end of the world, the general resurrection and final judgment was filled in by his medieval editors with material from his other works, particularly from his Summa Contra Gentiles.


The overall-plan is on the “origin-return”(exitus / reditus ) pattern of (i) one source of all being, differentiating into everything else, and (ii) the eventual return (or renewal, III, 91, 1, ad 4, Suppl.) of all things to their source, (cf. I,102,2), found in Plotinus (c.250), and others. But Aquinas reinterprets that outline and fills it in with (i) the philosophical story of a divine first, free, cause of all other things, including the stars and all life and especially of humans, (ii) overlaid and intertwined with the Judeo-Christian story of creation, sin, redemption, and the promise of eternal life with bodily resurrection, (iii) along with a divine law for humans and a divine plan for a future but certain everlasting Kingdom of God beginning on the Earth. He contemplates the end of the earth and of the stars, but without the destruction of the creation as a whole, and, instead, with its everlasting renewal.

How to read the work: The three Parts are divvied into Questions. Each Question is divided into component Articles, as sub-questions. Each Article begins with a succinct statement of key Objections to the expected answer, and a paragraph “On the Contrary” citing Scripture or some major thinker like Aristotle or a Father of the Church, expressing the general sentiment of Aquinas’ answer. Next is a section beginning, “I answer that”, known variously as “the answer”, ‘the reply” or “the corpus” [Lat: corpus: body] of the article, giving Aquinas’ position and reasons; that is followed by his numbered replies to the objections.

Every Article of the book follows the same order.. Even the longest Answers, like I, 2,3, (Part I, Question 2, Article 3) which gives the five proofs for the existence of God, and I, 76,1, on the union of soul and body, are no more than 1500 words, and Answers are often only 200 words; similarly replies to objections are usually brief, the longest perhaps 200 words. The Questions are organized so the general explanatory principles for the later Articles under each Question are laid out in the first Article, with more particular principles being added in the following Articles. Nevertheless, later Articles under a Question often contain the key philosophical issue: as do I, 2,3, and I, 75,2 (proof of subsistence of the soul); and sometimes Replies to objections do as well. The reader should explicitly decide whether the answer to each question is “yes” or “no” and “why” and what is the key philosophical (or other) reasoning on which the answer rests.

Aquinas answers questions, even the most particular ones, by placing them in a broad context, often of large-scale philosophical conflicts, say of Democritus, Plato and Aristotle, I, 84,6, and of Plato and Avicenna, e.g. I, 88,1, but concisely; and sometimes the philosophical reasoning is detailed, but brief, as on “whether the intellectual principle is united to the body as its form” I, 76,1. Some of the most important philosophical theories are developed in densely religious contexts, as when he develops the theory of relations and of names, in his exposition of the Trinity of Divine Persons, I, 32,2. For his overall task involves philosophical exposition and grounding of the elements of the Christian Faith amidst what is known by philosophy and other human inquiry as well.

Faith and Reason There are two basic sources of knowledge, that is, of ‘rational certainty as to what is so’: human understanding and divine revelation (I, 1). Understanding is the source of what we know for ourselves by reason, and revelation is the source of what were know by divine faith, that is, by divinely gifted trust in God’s Word, ( I,1, ad 1). The items can variously overlap for different people (II-II, 5). There is, of course, human faith, namely, all the forms of natural trust, that is, rational reliance upon others and upon the regularities of experience, that makes the fabric of human thinking, (and is subject to the vices of superstition and obduracy, lying, boasting, and the like, e.g. II-II, 109-111).

Some of the things known by divine faith (revealed) are also accessible to our figuring them out, and even proving them on our own, such as the existence of one immaterial God, that humans have free choice, and even the immortality of the human soul (psyche). But, as to the rest, he says, “we must not attempt to prove what is of the Faith, except by authority alone and to those who receive the authority; while as regards others, it suffices to prove that what the Faith teaches is not impossible.”(I, 32, 1; and I, 1,8).

There can be no conflict between Faith and reason (natural knowledge or successful science) because whatever is divinely revealed must be true and whatever is actually found out by human reasoning is also true. There are often apparent conflicts, partly from misunderstandings of what is revealed and partly from errors or inadequate reasoning or information in natural inquiries; proposed science is constantly revised. Moreover, humans are prone to take the objective appearances of things for the explanatory reality and, thus, to confuse what they understand partly for the whole of what needs to be known. (I, 70,1, ad 3); that happens in the conflict of untutored experience with science (I,67,3, Moses “out of condescension to their weakness ..put before them only such things as are apparent to sense”), often preventing real belief in the science and, reciprocally, inviting false reverence for its unstable speculations.

Philosophy and Theology. The intellectual disciplines, philosophy and theology, do not divide from one another exactly as do the sources of human knowledge, faith and reason, for theology involves both, whereas “philosophical science built up by reason”, although prompted and urged by religious faith, as it is by other pre-scientific convictions, is ‘finding out on our own’—what Aquinas called “truth such as reason can discover”( I,1.) and truth “known by natural reason”. It does not rest on authority from outside the community of science. Philosophy belongs to human science and consists of those things whose rationale humans can figure out entirely on their own, and includes all of the specialized sciences, as well as what we are rationally certain about that has not yet been organized into science, and or is unsuitable for it, like politics (statecraft) and art.

Theology, the science of things divine, has both revealed beginnings (e.g. that there only one God, maker of all else, who is a Trinity of Persons, and who participates in human history, etc.) and philosophical beginnings, (e.g. to establish that there is one God, creator of all things, and that the physical world is a complex of form and matter, and of act and potentiality, that there are four sorts of causes, that act is prior to potentiality, etc.). So the content of theology is mixed, where elements of revealed religious faith, which are its very first principles, are expounded and elaborated philosophically, and philosophical discoveries are adapted, complemented and supplemented with divine revelations (e.g. about the persons of God and the ultimate destiny of humans as individuals and as a species) to make up the one “wisdom above all human wisdom” (I, 1,6), which is “divine science” (scientia divina). Philosophy consists only of what can be found out by unaided human inquiry.

The overall Christian story that Aquinas underpins with his philosophical world view is: (1) that humans sinned, in some aboriginal catastrophe, The Fall, plunging all humans into a vortex of evil, both individual and corporate, for which no forgiveness was available before Christ, and from which the damnation and destruction of all human beings was eventually to ensue. (2) That in time, God the Father made a gift of his Son to be a human, Jesus, (3) who, by a perfect act of love of all humans and of obedience to his Father’s Will, offered his own life, taken by judicial murder, as a sacrifice (a key element of worship from the time of the children of Adam, and foreshadowed by Abraham’s offering Isaac), that made forgiveness available to all humans, and who rose by his own power from the dead, as the “first born of a new generation”, thereby offering all humans (4) who accept faith in Jesus the Redeemer, the prospect of life forever with God, and (5) establishing an earthly institution, his Church, the People of God, to continue offering that sacrifice, and sharing in the Bread of Life, and in the aid of the Sacraments,(6) working for human society in accord with divine love, (7) until the “Second Coming”, the return of the Redeemer, the resurrection of all who have died, and a final judgment of all mankind, and (8) the establishment of the divine community of humans (the Kingdom of God), and (9) the “life of the world to come”.

That story, with elaborate details and interpretations of past and future human history is embedded by this work in the philosophical conceptions of Aquinas’ philosophy, to make one overall fabric of human wisdom, that is, one overall account of the nature of reality, of man’s place in it, and of the course and outcome of human history: the story of God and Man. That is what is presented with detailed rationales in this book, though of course, not all the details, even all the ones Aquinas worked out elsewhere, are contained in this one book.

The Philosophical Sources. Aquinas is usually regarded as an Aristotelian, having been one of the major interpreters and adapters of all of Aristotle’s philosophy, and central to its introduction to the Latin West in the mid 13th Century. And indeed the overall outlines of his philosophical scheme, and most of the content and of the explanatory general principles he uses, are adapted right from Aristotle. But there are crucial alterations in Aristotle’s presuppositions, some to fit the demands of Christian belief (such as a temporal beginning of the world and personal immortality), and some original and basic philosophical changes, particularly his notions of being and existence.

Some of those changes, especially in the metaphysics of transcendental being, have Platonic and neo-Platonic origins ( in Philo, Plotinus, Porphyry, Pseudo-Dyonisius, St. Augustine, and 12th Century writers, like the School of St Victor); and some have Stoic sources, especially concerning the passions and moral virtues, while others originate in Roman Law (elements of his theory of law) and in Sacred Scripture (about 100,000 citations) like his notion of persons. Others still, like the absolutely basic claim of a real distinction between essence and existence in all finite things, originate in response to the Arabic philosophers from the 9th to the 13th centuries, Avicenna particularly, while still others come from Moses Maimonides and other Jewish thinkers, and many, many more come from St. Augustine, Boethius, Abelard, and other medieval Latin Philosophers (about 5,000 other works are cited overall).

The philosophy of the Summa is not a mélange, a salad of others’ ideas; it is an original and unified construction, like a cathedral with many integrated styles and influences, but one overall plan. The crucial architectural elements show up right in the beginnings, in the Treatise on God (I.1-27), and are elaborated in all that follows: that there must be one thing that exists on account of itself, in which being and essence are the same. The overriding philosophical theme is that God is ipsum esse subsistens, the one and only self-subsistent being. That all other being is caused, dependent and is both actuality and potentiality in various respects; that all finite being is made and sustained by God, aimed at God as it final cause and that humans, the highest animal creatures, are by nature aimed at happiness, which, however, cannot be concretely and perfectly achieved without divine supernatural intervention.

On God’s Existence and Nature.
Like Augustine (c 400) and others, Aquinas expands the ancient Greek idea of a divine being that is the divine ultimate explanatory principle of all being, into a notion with elaborate religious content: the Judeo-Christian belief that there is a loving, omnipotent and free being, the one object of worship and sacrifice, who gives a divine Law for mankind, and has an indefeasible plan for human history and for each human.

The key philosophical step is to show that besides being a logically necessary explanatory condition for the existence of all things perceived, the divine being must be intelligent, free, good and loving, in order to cause and sustain the universe (cosmos, world) that might not have been at all (i.e., that exists contingently). So the essential departure from ancient necessitarian views is that everything of the perceivable world might not have been at all, and that the ancient materialists (Democritus, Empedocles) were wrong too, just as Plato and Aristotle had thought as well, to suppose that the perceivable world originated by chance from necessarily existing particles. The result is that there must be a cause of being that exists necessarily and acts freely: otherwise there could be no contingent being at all. For whatever a necessarily existing being causes by nature, exists necessarily as well, even if not on its own account (as Avicenna, c.950 had explained). From that base, the more ‘personal’ attributes are then deduced, and religious features are anchored to it.

Such freedom to create the perceived universe logically requires, intelligence, omniscience, omnipotence, freedom of action, moral agency, goodness, love, and willing conservation to keep all else in being. Aquinas provides the argumentation to establish each of those outcomes as a necessary condition for the existence of anything other than the divine being (God). The key step, once the existence of some primary being (God) is established, is for him to show that what-it-is (its essence) cannot be in any way different from its being (esse): it exists on account of what-it-is.

Aquinas disposes of whether it is self-evident that God exists by saying “Not to us”, though if we knew by direct acquaintance “what” God is, as we know by perception what a triangle is, then God’s existence would indeed be evident, just the way “ a triangle is three-sided” is evident from perception. But we don’t perceive or intuit God.

However, the existence of God can be demonstrated (proved); but not a priori, that is, not from something explanatorily prior to the conclusion. Rather, it is proved a posteriori, as a reality required for perceived effects that are experienced by us: motion, change, causation, contingency and order. Such are the perceptions from which we begin to inquire: namely, the things in the perceived universe that might not have existed at all; for nothing comes to be without a cause.

So the “proofs” consist in identifying realities that logically require a cause, or broadly, an explanatory condition, and showing that the required kind of cause is something “everybody calls God”. Thus, first he tells how to prove the existence of a cause that is the divine being, and is commonly called that. Then he tells how, further and formally (I,2-26) to identify that being by its attributes as the God of religious worship and faith. He does the existence proofs in one Article of about 1200 words. (That may be the origin of the phrase, “a proof, one, two three” for quick decisive argument; for the article is I, 2,3.) The divine nature, however, takes 25 Questions I (about 140 pages).


He calls the existential proofs “ways” because he is sketching classic reasoning, found in Aristotle, Plato, Avicenna, and Maimonides, not providing all its details; for instance, the argument to a first cause of cosmic motion is found lengthily in Aristotle’s Physics. We summarize the “third way”, the contingency argument here:

Some things exist that might not have existed at all (contingently). But it is impossible that everything be like that. For on that supposition, there might (possibly) have been nothing at all. But, if there had been nothing at all, nothing would have been possible. But something is possible, because things are actual. So there can be (could be) no condition under which nothing is possible. Thus, the supposition that everything might not have been, conflicts with a self-evident truth, that something is possible (exists). Therefore, not everything “might not have been at all”: so, there must be something that cannot not-exist, namely something that exists necessarily. But that is the thing people call ‘God’.

The objectors primarily say, ‘maybe things really did come from nothing’, and ‘maybe each thing might not have been, but not all of them, altogether’. The latter, raising the ‘fallacy of composition” objection, is irrelevant, because Aquinas is using the modal logical principle that any conjunction with a contingent member, even only one, is contingent and, therefore, might not have been so. So any conjunction of contingent beings, no matter how many, as a whole, might not have been at all. And thus an explanation is needed for its being.

And the former denies the obvious. Aquinas’ thinks ‘no thing [say a star] comes to be without a cause’ is known for certain. Nothing comes from nothing. Thus, those objections simply suppose what we know, not to be so, and are thus, contradictory to known truth. (Of course, Avicenna (c.1000), thought the order of apparent causes emanates necessarily from the being of God, and so nothing is contingent as Aquinas and the Christians supposed: basically Avicenna denied that it is evident that if a thing does not exit on account of what-it-is, it might not have existed at all).

The second of his “ways”, that the beginnings of contingent things require an unproduced originating cause is like the one above. The other arguments for the existence of a First Being are structurally similar, though the general premises, that cosmic motion/change has to have a, relatively, unmoving cause (Aristotle), that less perfect things are explained by more perfect ones (neo-Platonism), and that the intelligible order of nature must have an intelligent explainer (Augustine and, perhaps, Aristotle), are more contentious and specialized, and may involve cosmic analogies. But the basic reasoning is that it is impossible that we have a universe such as we perceive unless there is a necessary being, a first cause of whatever begins to be, a cause of the diverse degrees of perfection, and a designer of the intelligible order of all of nature. Just consider the last one: if the cosmos is inexhaustibly intelligible, yet might not have been at all, then whence the intelligibility, and whence the Laws of Nature?

As to change (cosmic motion) and coming-to-be, Aquinas says an infinite regress of all-together causation is impossible. His reason is that you would never get to ‘here’, to any particular perceived case now, if you had to run through an unending (infinite) sequence of predecessors; that is transparent because by supposition it is not ever completed; (any more than you could have arrived at a particular coin flip by going through an infinite run of prior flips because you would not, ever, have arrived “here”, always having further to go).

The Divine Nature. Aquinas provides a far more elaborate inquiry (I, 2-25) into the nature of the divine being. The question, “what features are required on the part of a necessary being to explain the existence of contingent being?” is common to each stage, and the form of argument each time is “indirect proof”, namely, to deduce an inconsistency between denying the proposed divine attribute and the conclusions already established.

Simplicity. A basic common premise in those steps is that ‘whatever is a composite of actuality and potentiality, is contingent, causable and in need of an explanation’. Thus, a First Being cannot be composite in any way: of parts, of components, of multiplicity, or even of really separate traits, like knowledge and power, or knowing and choosing. Rather, such a being is entirely simple: it must not be a composition of distinct act and potency (that is, of capacity and its realization, or of ability and its exercise, or of possibility and actuality) in any way whatever, because that would defeat it’s existing on account of itself (already established by I, 2,3). For what exists on account of itself exists because of what- it-is, without any further explanatory feature.

We can know that God exists on account of what- God-is, without being able to know what-God –is (the divine essence); for God is incomprehensible to any creature; --not that God is unintelligible for we can understand a great deal about God; but we cannot know, as we can, say, with a triangle or a chemical element, what- it-is.


Being and Essence. In everything else, what-the-thing-is is really distinct from its being (existing) because a separate cause is required to make it come to be. But in God’s case, being and essence are really the same: there is no additional explanatory factor. That is sometimes called, misleadingly, nowadays, “identity of essence and existence”; but, of course, what Aquinas meant was not the de dicto, ‘everything true of the divine being is true of what-God-is’ (for we know that God exists and do not know what-God-is); but, rather, de re, there is no difference of reality at all between what God is and that God is, because there is no additional explanatory factor for the divine being. With everything else, there is a real distinction between what-a-thing-is (essence) and that-it–is —namely, that there must be an additional explanatory factor for there to be such a thing, a cause; for instance, no dog exits on account of being canine but, instead, each requires a producing cause.

From the denial of any difference between the being and essence of God, the major elements of the divine nature follow: simplicity, first, as above, and then, immutability, intelligence, will, freedom, power, omniscience, omnipotence, and eternity, each by indirect proof. For, supposing the denial of any of those, contradicts the real sameness of the divine being and essence by requiring some additional explanatory factor and some composition of (unfulfilled) potentiality with actuality.

The apparent multiplicity of divine attributes is entirely the result of the human manner of conception and definition based upon physically perceived things: “ we always name a thing as we understand it” I, 32,2. Divine attributes are multiplied according to the plurality of human conceptions, not according to distinctions of divine being. In fact there is no difference in reality among God’s knowledge, power, being, will and any other divine perfection. So that opens the question (I, 13) of the meaning of the words applied both to creatures and to God. Are they different in meaning?

Analogy of Meaning. All words that apply to God, like ‘knows’, loves’ and ‘judges’ are captured in meaning by the context of divine being and, though remaining the same in word-definition (idea), in contrast to different words (the way ‘loves’ contrasts with ‘knows’), the manner of meaning (Lat: modus significandi) contrasts with the application of the same word to any finite thing. It is somewhat the way waited for differs in ‘they waited for the dawn’ and ‘they waited for the bus’ and turned red contrasts in “The sky turned red at the sunset” and “He turned red with embarrassment.” There is contextual adaptation of what is meant to the different sorts of things involved (I, 13,5).

Thus, no word is univocal (exactly the same in meaning) between finite things and God; but the difference is systematic and not haphazard as it is with equivocals like ‘bank’ (for money) and ‘bank’ (for turn). Moreover, that linguistic phenomenon, contextual adaptation, is very general in our languages, and has several other linguistic forms, as in healthy/dog; healthy/diet, as well as metaphor, sowing/seeds; sowing/ lies. Both Aquinas and Aristotle make analogy of meaning a central tool in everywhere their philosophy, apart from its religious applications.

The analogy of word-meanings tracks the analogy of beings (of reality), through our analogous thinking (Lat: analogia rationis)—the sort of thinking tested nowadays by Millers Analogies Tests. Aquinas reasons that a creature cannot be said to exist in the same sense as God does, because its being is derived, participated (I, 44,1), whereas God is what-is-because-of-itself (ens per se subsistens).

The underlying idea is that human concepts are abstractive responses to realities, and as the realities differ proportionally in manner of being and causation, so do our conceptions for them; and since the meanings of words are concepts, and the meanings differ as the concepts adjust. Thus analogous realities are thought of with analogous concepts.

So Aquinas does not think all words applied to God, like ‘loves’, ‘understands’, apply only negatively to eliminate the error of saying the opposites (Maimonides) (I, 13,2); or, that when they are used positively, they apply only ‘symbolically’ or ‘metaphorically’ (Maimonides) (I, 13,3), as in “God is the lion of Judah”; but many apply literally, but analogously to other literal applications to things we can perceive (as with ‘turned red’ above). That is, it is literally, but analogically true that God exists and knows and loves the world (I, 13,3); and God is correctly characterized reciprocally from relations things in the world bear to God (I, 13, 7, ad 4), but without standing in any real relationship to the world (I, 44,3). That deserves a pause.

Real relations to God but not vice versa. This is a central idea, one that eliminates many apparent paradoxes about God’s permanence, knowledge, will and timelessness. Other things are really related to God: as effects, as dependent, imperfect, created, temporally ordered, foreknown, willed, planned, etc. But God stands in no real relations to other things at all. Not even by creating, sustaining and governing the world.

Now the 13th Century notion of a real relation involved much more than that a relational word truly applies to some group of objects, say ‘being near,’ ‘being married to’, being a child of’, ‘being the square of’, or ‘being known by’. Some of those are real relations, and some are merely “rational” or “logical”. A thing has to begin to be, cease to be or change to come into a real relation to another (I,46,3 ad 1); all change, beginning and ending, is in things other than God (I, 45,3). .

The same hold for divine knowledge, foreknowledge of what is future to us, and predestination, providence, and even final judgment: the reality of divine activity is in the humans’ being-judged (and rewarded or punished), known and made; they undergo a change. There is no future to God who is unchanging, omnipresent by being and power and will, and to whom all is present at once. It is all his present, and his doing, just as your present consciousness, and all its contents, is yours, continuously dependent on you, and would all disappear instantly with a change of your attention. Aquinas quotes St. Augustine, who says: “if the ruling power of God were withdrawn from His creatures, their natures would at once cease, and all nature would at once collapse.” (I, 104,1).

Divine conservation is sometimes also called “continuous creation” for the act is the same, except in definition of the word, as to make things be at all. Aquinas does not, however, reject the pious practice of believers who describe God as if God had already seen (in a common time) what will happen and already decided (as if in our past) who is to be saved, etc. Yet Aquinas is very clear that in the science of God, God does not change, does not have any temporal relation of past, or future, to anything else at all. It would, perhaps, have helped the perplexities of believers, if Aquinas had said that strictly, such claims about foreknowledge and predestination, are not true, as his theory requires. It seems that he allows the discourse of piety as discourse according to the objective appearance, but not the science, of things. (Cf. I, 67).

God knows whatever can be known, all together in one awareness, but not with knowledge caused by things, as what we see is caused by the things we see; rather God’s knowing causes things to be (“the knowledge of God is the cause of things” I, 14,8); for God’s will and knowing are really the same. So too, all our future, as all our past, is relative to the temporality of human experience and also to the physical succession in nature (cf. III, 91,2 ad 8). But, for God, it is all “now!.” “God knows contingent things not successively, as they are in their own being and as we do; but all at once.”(I, 14,13). So divine foreknowledge is a description of God’s knowledge from our vantage in experience; so is predestination. So puzzles arise from confusing our progressive experience with God’s awareness. God knows whatever is, and so, knows what will be for us, but not ‘now’ because God does not, by nature, share a ‘now’ with us.

The Goodness of God and the Origin of Evil. In so far as anything has being it is intelligibile (“true”) and, suitable for rational desire, and so, ontologically “good”, as both Plato and Aristotle held, as well. The ontological goodness of things is their rational desirability. Therefore, an evil is “a missing good’, a privation ( I, 48,1), the absence of good that ‘ought’, either naturally or morally, to be there,. It is privation, like blindness in a person, not mere absence like blindness in a stone. Natural evils, like animal blindness, suffering and death, lethal earthquakes, tornadoes, and the like, are only incidentally evil, that is, locally and relatively undesirable by affected creatures, (if they are not caused, like some plane crashes, say, by immoral acts).

Nothing, in so far as it has being, is or can be evil. It is not possible for God to make something that is less than it ‘ought’ to be. For in so far as it is made, the thingis rationally desirable. “Nothing can be essentially bad”(I, 49, 3). Further, there is nothing that absolutely ought not to be, not even the worst evil actions of free rational creatures. Still (I, 49,2), God can be the cause of what ought not to be, by causing a penalty fitting to justice (I, 49,1), for creaturely wrongs, but never can, as angels can (I, 63,1), and humans can, cause evil by fault (I, 48,5).“Every evil in voluntary things is to be looked on as pain or fault”(I, 48,5).

He reasons that it is within the perfection of a divine agent to make a created order in which the natural and imperfect causes produce effects that people deem evils, like plagues, pestilences, bugs and beasts that harm us; for, of course, finite causes will be imperfect agents. Therefore, the “order of nature requires that some things can, and sometimes do, fail” (I, 49,2). At I, 22, 2, ad 2, he says, “hence, corruption and defects in natural things are said to be contrary to some particular nature; yet they are in keeping with the plan of universal nature”; and he reasons that “a lion would cease to live if there were no slaying of animals”, thus acknowledging that biotic life requires death, that it is not a defect for God to create carnivorous and vicious animals, and poisonous snakes. Human suffering and death is another matter because it is the result of Adam’s sin which incurred the loss of an extra-natural divine protection in which human persons were first created (I, 97,1).

So, genuine evil requires what ought not to be from that cause. But God’s will is the cause of good in all things, because being and goodness are the same (I, 20,2), and things are good because God loves them, not vice versa: “the love of God infuses and creates goodness”. But “it is of the essence of evil that it is the privation of a good” (I, 14,10). Hence God cannot be the cause of evil as such. “Evil can only have an incidental cause; hence reduction to any per se cause is impossible;” so, there is no intrinsic principle of evil, no anti-god; even Lucifer (Satan) is a creature gone wrong. And moral evil is caused incidentally by created free agents acting for what they deem to be goods, angels acting to enjoy pride; or humans, acting for pleasure.

And furthermore, no one rightly says such freedom ought not to be at all, because without freedom, nothing among creatures could be right or praiseworthy. And there is no evil from which God cannot bring divine good: forgiveness, redemption and salvation. The innocent (e.g., Abel, Gen. 20) cannot be really harmed, but are in the bosom of God, while the evil-doer faces eternal death, repudiation forever by God, destroying himself.

Is it better that there be no evil by there being no creature able tofall from the good by its ability to do good, or for God to bring good out of evil, no matter what humans do? “Christ’s passion was sufficient and superabundant atonement for the sin and debt of the human race” (II, 48,5), not just for the fall of Adam, but for all the terrible evil of mankind, ever to come. The latter is Aquinas’ conviction: that divine forgiveness and gift of eternal life ‘makes good’ out of all the evil there will ever be. The human measure of divine mercy is the magnitude of human evil.

Aquinas, like Augustine, thinks it is contradictory to say a creature has freedom but can do no evil in its earthly condition, even given that it has a divinely assisted holy will; for that would take away the indeterminacy of the agent between what is good and what is not, and so, would have to presuppose the presence of a completely fulfilled will that is not naturally possible.

In addition, Aquinas envisions a cosmic drama, larger than Earth’s history, involving evil among the angelic spirits (demons), e.g. Satan (Lucifer), “for the motive of pride is excellence”(I, 63,8) and is “worst among the best” (I, 63,7), as dramatized by Milton, and painted, for instance, by Peter Bruegel (c. 1560), “The Fall of the Angels”. He treats the Earth’s story of salvation as one that displays the perdition of the demons by their evil agency (I-II, 80), their envy of humans for God’s incarnate love, by their exacted and frustrated faith (II-II, 5,2), and by their participation in human evil (I, 104-114).

Angels. Prompted both by Aristotle’s speculation that the stars are moved by intellectual spirits, by Platonists (cf. I, 63,7) who believed in supra-earthly beings, by Scripture, e.g. Daniel Vii, 10, and by spiritual writers like (pseudo-) Dionysus, Aquinas wrote (I, 50,3) that there are innumerable created immaterial spirits (angels). Just as “the heavenly bodies…exceed corruptible bodies almost incomparably in number; for the entire sphere of things active and passive is very small in comparison with the heavenly bodies,” so also, “immaterial substances {intelligences} exist in exceeding great number, far beyond all material multitude” even of the heavenly bodies. For, “the more perfect things are, in so much greater an excess are they created by God”.

From the 24 Questions on Angels (I-50-74), already mentioned, and the later exploration of angelic being, of their being human guardians, and of the agency of demons (I, 104-114), it seems that Aquinas considers the Earth to be a small part of the natural drama of the cosmos, just as it is of the created things of the cosmos. But from a supernatural religious standpoint, the Earth is the locus of a most extraordinary, personal and permanent divine activity: the special creation of man, the fall, incarnation, redemption, and salvation of humans, with the coming Messianic kingdom, and a universal judgment and transformation of humans forever.

But such entirely immaterial things, the angels, must be intelligences with free choice, and, furthermore, cannot differ from one another materially, and so, have to differ in species, (I, 50,4). Therefore, one angel differs from the next as much as a human differs from a dog: “it is impossible for two angels to be of the same species”; “ all the angels differ in species according to the degrees of intellectual nature” (I, 50,4, ad 1.). The innumerable angelic species indicate how far God’s being exceeds anything humans can perceive. Aquinas draws out his philosophical principles to answer questions about their powers of understanding and will, their memory, knowledge of one another communication, the relation of such spirits to bodies, to movement, place and time, and to error, wrongdoing, and its relation to human evils (I-II, 80,2, and I,106-114).

Man: Human Nature, Powers and Fulfillment.

All material things of any kind are composites of form (structure) and matter (stuff out of which). The form determines the “what” and (internally) causes the thing to exist (as a shape causes a statue to be, until it melts), and the matter, the stuff, clay or gold, limits and individuates it. So a crystal may consist of molecular parts (matter) structured (formed) to behave a certain way chemically, like salt. Form, structure, is the intelligible feature of the physical, --what can be understood and represented by humans in a formula-- and is the explanation of what each thing is able and disposed to do. Thus, as we know now, there can be “on-off switches” mechanically, electrically, magnetically, and molecularly and even biologically, and, so, in principle, can be such computers. The form ‘on-off-switch’ is realized in each: as Aristotle said, “the same form can be received in many kinds of matter”.

All earthly living things, plants and animals, are composites of a form capable of causing life and action, called “soul” (psyche), operating in matter suitable for life (say, carbon molecules). Humans are a special case of living things: rational animals who are persons. Thus, they are a composite of soul (psyche) and body. But people are not two conjoined things; for rationality is not added to animality as a power of it, as Locke later supposed, but is a manner of animal being. Being human is a kind of being animal.

A human is a composite of a material basis (Aquinas called it flesh and bone (nowadays, perhaps, “cells”), organized by psyche (spirit/ soul) into a single animal that is able to understand and to choose its actions. “The first thing by which the body lives is by the soul” (I, 76,1). When Aquinas says “man is a composite of soul and body,” he means ‘body’ as ‘matter capable of human life’, not, ‘living thing with organs” that already supposes a soul. And he is speaking of soul (as it were, software) as the organizing form that makes the human alive and to operate as one single thing, a thinking animal. (What was for centuries hard to grasp is commonplace now: software that makes a thing what it is, and to do what it does: that is form. And soul is a kind for form.)

He thinks the soul not only provides the composite with abilities, like a program with sub-capabilities, but in humans the soul also has its own manner of being, “subsistent being”, which it “communicates” to the composite. The being proper to the soul is the being of the composite. (In other living things, the soul is formal cause of the being of the composite, but has no being of its own; it is “hard wired” and destroyed with the composite, as is the shape with the triangle.) When a human dies, as with animals, it dies all over all at once; but the human soul is separated and not destroyed, because it has existence on its own.

Why is the human soul subsistent (actively existent on its own)? (I, 75,3) That manner of being is required for the defining operations of the intelligent soul, understanding and choice, (I, 75,2). Aquinas thinks the immateriality, and thus immortality of the human soul is proved from the fact that “understanding is not possible through a corporeal organ” (I, 76,1). The understanding has to be actively able to be in an unlimited (infinite) variety of states (say, to understand any one of an infinity of arithmetical truths, or sentences of one’s language) and so, cannot be restricted to the physical states of any bodily organ. For no material power, sight, hearing, imagination, or the like, can be in an unlimited variety of states. Aristotle formulated that reasoning, De.An.iii.4. Thus, the understanding can do what cannot be done physically. Therefore, the psyche “has an operation and a power in which corporeal matter has no share whatever” (ibid).

His reasoning is this: “It is impossible for it [the soul] to understand by means of a bodily organ since the determinate nature of the organ would impede the knowledge of all bodies,”… “therefore, the intellectual principle which we call the mind, or the intellect, has an operation per se apart from the body. Now only that which subsists [exists on its own] can have an operation per se” [that is, by itself and on account of itself]. Why must the immaterial soul have subsistent being? Because the manner of being must explain the manner of a thing’s operation (I, 75,3). If it acts on its own, it must exist on its own. Otherwise, something comes from nothing.

All the powers of a living thing have the soul as their one explanatory source; otherwise, there would not be one, single life. Such a program must have many sub-parts, because the “powers”, or ‘faculties” are distinct. Aquinas distinguishes and determines the order and causal interactions of such ‘powers’ (see below).That is his cognitive psychology, as it as Aristotle’s. Some abilities are found in all living things (nutrition, growth, reproduction), and others are found in animals generally (sensation, imagination, memory, perception, and action from desire). But some are definitive of humans, like understanding (intelligence) and will. Intelligence transforms all the animal powers (even aspects of the nutritive, reproductive and growth powers), by unifying them into one intelligent life.

The powers of understanding and will are also affected and incidentally limited by the bodily states of the human, e.g., its health, pains, pleasures, hunger, passions, suffering and death. One can’t think of much else, if hungry enough. And one can be absorbed in thought. The living body is the human, the person. Aquinas is thus, not an Augustinian or Cartesian dualist.

The Causal Chain in Human Knowing. Basically I, 75-90 is “generative” cognitive psychology; that is, it is “black box” reasoning, mostly taken from Aristotle, to determine the abilities and their intermediate causal connections and outputs (e.g. “sensible species”: appearances) that are required for animals, and particularly, humans, to behave as they observably and introspectively do.

So we count the external senses of animals from their discriminatory response abilities, to color, taste, touch, smell and sound, and count the internal senses from the distinct abilities required for perception and action, namely, imagination, memory, coordination of senses, and estimative ability. Those are needed to do what animals do and what we can tell we do: remember, imagine, unify multiple sensations into one appearance (the ‘common sense’ sensus communis), and gauge and proportion the motion of limbs, eyes, muscles, etc, and intuitively estimate strength and effort to be expended, as in a horse’s jumping a fence (estimative/cogitative power). Natural estimative abilities are also subject to learning in higher animals, and to feedback from understanding in humans. All those abilities amount to the perceptual and behavioral abilities of animals.

The ‘representationalism’ of Aquinas belongs only to the conjectured stages of the causal chain from physical objects to perception and understanding (and back). But the output of perception is the presence of things to animals: hawks see mice, by means of representations (“sensible species”), not by seeing representations of mice and somehow ‘inferring’ to the world.

The outcome of cognitive psychology for Aquinas is direct realism about animal perception and human truth: namely, what animals, normally, see and hear and taste and touch, is what is real. And, most importantly, when what we think is true, what we know is what is so. With Aristotle he holds, not what is nowadays called a correspondence theory of truth (though he describes the causal process that way, as a series of causes and effects, producing resemblances, e.g., I, 85, 5), but an identity theory of truth for the outcome: the understanding becomes what it knows: “as regards things actually understood, the intellect and what is understood are the same” (I, 87,2). And in I, 79,5 ad 2, he quotes Aristotle with approval: “Knowledge in act is the same as the thing”. What we understand, when we are right, is what is so: when I know you are here, what I know is that very reality.

In animals, and so, humans, there are drives, called appetites. One is a constant bias causing pleasure and avoiding pain (the “concupiscible” appetite), and the other, in crises, directed by instinct, overrides the first, and causes flight or fight to preserve the animal (“irascible” appetite). These are constant causes of all animal action, whether perception, movement, or even sleep and dreaming, and determine the operation of the senses as well as behavior.

Every sense is a form of pleasure (and displeasure, as well): “every sense is a mode of love”. Perception, which is more than sensation because it is a presence of ‘the other’ to the animal, requires imagination (of things sought or feared), and memory of the expectations aroused. Imagining is not typically by picturing, but is a particular readiness that perception of the object relieves, as when something lost is sought. So imagination does not require belief, but is expectation, readiness of a certain sort.

The normal living of animals is active, from the pleasure in the acting, and avoiding pain, and fulfilling desire (which requires imagination). Mice scurry because the can; animals eat because the want to. Higher animals, like horses and dogs, are said by Aquinas to have an “imperfect voluntary”: that is, such animals do what they want to do because they want to, but, unlike humans, without any grasp of why they are doing it or awareness that they want to. They act “ with “imperfect knowledge” of the end for which they act, “through their senses and estimative powers,” “without knowing it under the aspect of an end”,(I-II, 6,2), and so, without any control over what they want (I-II, 6, 2, ad 2). Still, in the training and use of animals, it is their “imperfect voluntary” that is habituated by rewards and aversions. In humans, the animal desires and powers can be corrupted by human intelligence, as well (e.g., into greed, lasciviousness, perversity, bestiality, cruelty, etc.). In humans it is not the animal powers that corrupt, but reason that corrupts the animal inclinations.

Human Reason. The rationality of humans consists of three basic abilities, three powers of the psyche, whose operations are (i) conception, (ii) judgment and reasoning and (iii) choice. The first is the “abstractive” understanding, variously called “the active intellect” (intellectus agens), or the “making intellect” because it makes conceptions out of sensation; it is the active, always “on” ability to separate the forms, the intelligible structures, of things from their particular matter, making conceptions. Thus a human does not see an object just as a physical particular, under no interpretation at all; even in a flash, it is a “what?.” Active conceptualization, the first step of understanding, is something humans do, willingly, but by nature and always.

Judgment. The second constant intelligent activity is judgment, typically the combining of conceptions into commitments to perceived reality, for example, ‘that house has red trim’, or ‘there isn’t anyone standing in front of the house”. The most basic form of judgment is a constant reality commitment, an existential commitment, usually accompanied by habitual affirmation of appearances.(Aquinas does not discuss the varying vividness of such commitment or its willing suspension, for stories).

The ability to make judgments and to reason with conceptions, in response to reality presented by appearances, or imagined or remembered, is called, by awkward translations from the Greek and the Arabic, the possible intellect (sometimes, by Arabic writers, also “the potential intellect”), roughly, ‘the capable understanding’. Such judgmental understanding is also ‘always on’, requiring only conceptions along with sensation, for its activity. Its states are our beliefs, our convictions, and our reasoning. When true, the content of the states is the reality known.

Will. The third intellectual power is the rational appetite (will): the will is the constant cause of activity in pursuit of something wanted (some ‘good’). It is causation that consists of a constant leaning to satisfaction from what we choose (e.g., to get the thing you chose). Abstractly, that bias is toward fulfillment, toward what Aristotle called “happiness”.

But that inclination is opaque, to get what one decides on. It is without a concrete object; and so, it is dependent upon our appraising the promise of options ‘to which the will is indifferently disposed” (I-II, 6,2 ad 2). Thus, an unlucky person can be constantly mistaken in what he seeks. A vicious person, rancorous, or badly trained, can constantly mistake relief of desire for satisfaction, like a person imprudently scratching an itch he makes worse.

About options to which the “will is indifferently disposed” (I-II, 6,2 ad 2), a person can deliberate. And one typically terminates deliberation by decision: that ability is to reach decision from indifferent options is freedom of will. Such decision aimed at “getting one’s way” can, and will if repeated, originate patterns, habits, of action, either in accord with reason (virtues) or opposed to it (vices). “Those actions are properly called human which proceed from a deliberate will.”(I-II, 1).

Freedom of choice, as an ability, is both a necessary condition of action in accord with understanding and for the fact that humans, unlike animals, are subject to moral praise and blame (I-II, 6,2 ad 3), that is, to judgment as to whether they act rightly or wrongly, in contrast to merely well or badly, as with horses or dogs.

Do humans seek happiness? In the abstract, yes, because they always want what they choose. But do they always want something? Yes. “All human actions must be for some end”. But is there one end for which humans always act? Yes, Aquinas says, all human action is essentially ordered toward one end, happiness; that is because “to desire happiness is nothing other than to desire that one’s will be satisfied,” (I-II, 5,8), which we do by nature in whatever we do. So, he reasons, “ it is impossible that one man’s will be directed at the same time to diverse things as last ends”(I-II, 5). Even what is in other respects evil, is always chosen under some respect in which it is a good: for pleasure, power, excellence. And anything sought as a good is either sought as a good in itself or as an intermediate to some good (I-II, 1, 6). So there must be a last end that is the aim of appetite and that is the aim of all intermediates: happiness, a state of having one’s will fulfilled. Opaquely it is what ends the constant pursuit (I-II, 2,7), namely, that our wills be satisfied.

Such a satisfaction has to be permanent, and consist in active understanding and enjoyment. So it is not naturally available. Only life with God is happiness, and it is attained, by those who do, by knowing and loving God (I-II, 1,8), not by any created good (I-II, 2,8); it is the direct vision of God (I-II, 3,8) that causes delight (I-II, 3, 4 and 5). The present life is limited to various forms of flourishing, and that is uncertain and transient (III, 75, 1).

Immortality and the possibility of resurrection. Immortality, as indestructibility of the soul is not sufficient for human personal survival of death. For the soul, even though per se existing, is not the person (III, 75,1 ad 2), but a part, requiring individual embodiment for a complete human. “Abraham’s soul properly speaking is not Abraham himself, but a part of him;.. there needs to be a life in the whole composite, soul and body” (III, 75,1 Supp. Ad 2). So, it has to be possible that humans are resurrected for it to be possible for humans to survive death. Since possibility does not follow from conception alone, such a possibility cannot be demonstrated by appeal to God’s omnipotence, but rather is presupposed by it.

Aquinas does not offer reasoning that is independent of revelation, to establish the possibility of resurrection. His philosophical reasoning goes only this far: the human spirit (cf. I, 97,3), is incorruptible and naturally immortal, and the soul (spirit) is not the person (III, 75,1, ad 2). And, also, that it would be incoherent for a part of persons to survive, forever naturally incomplete, and not suitable for the rewards and punishments fitting for one’s life but belonging only to the composite substance (III, 75, 1, ad 3). That amounts to a weak likelihood. The rest has to be settled by divine revelation; for such a vast material change, from dust, mud, or ashes, or from parts of cannibals, to a restored living body, lies only in the miraculous power of God (III, 75,3). He seems to take it as sure that such a transformation is not within the power of nature, as is metamorphosis. Nevertheless, as theologian, replying upon Scripture, he concludes, ‘the soul cannot have the final perfection of the human species so long as it is separated from the body. Hence, no soul will remain forever separated from the body.”(III, 75,2 ).

Man: The Regulation of Human Conduct: Internal: The morality of human actions depends on their being voluntary (done from desire in the absence of defeating ignorance, fear, violence or passion); voluntary actions are either habitual or deliberate (chosen). The measure of objective moral permissibility (right or wrong, not tied to the praise or blame of the agent) of a sort of action is whether such an action is in accord with reason used rightly. The same test applies objectively to the intention, circumstances and foreseeable consequences of the act. The measure of subjective moral permissibility (praiseworthiness or blameworthiness of the agent) is: a permitted intention, and a reasonable belief that the action is right in itself, and under the circumstances and in its consequences. The overall “goodness” [rightness] of action is from an “integral cause,” that is, from its being both objectively and subjectively good; (i) the intention, (ii) that sort of act (objectively described), (iii) its circumstances and (iv) its consequences, all have to be in accord with right reason, both objectively and subjectively.

And the content of right reason as to action and its circumstances is determined by a fit between human nature, one’s circumstances, resources, and aims, all measured by human reason. That fit is objectively regulated by moral law; hence, Aquinas’ philosophical moral theory is called “natural law morality”, see below.

Virtues and Vices. Human action is typically habitual, though the most important acts, including the ones that initiate habits, are deliberate choices. Habits are constant tendencies to action, a constant causation; some are natural, like bold temperament, or timorousness; some are acquired, by training, or by self-discipline, like studiousness; others, by self-indulgence, pride and gluttony.

Habits in accord with right reason and are called “virtues” and others, acquired from impermissible choices or from bad training, bad example, or by self-indulgence, are persistent inclinations toward action contrary to right reason and are “vices,” like greed, covetousness and envy. Aquinas sorts and orders the wisdom of the Greeks and of the Stoics, as well as the content of Roman Law, into an elaborate classification and analysis of the virtues and the vices, arranged under the classical “cardinal [hinge] virtues”, of prudence, justice, temperance, and fortitude, and, further, with religious inspiration, under the theological virtues of faith, hope and charity. Those are just the headings; the classification is detailed and full of examples.

In each case, he considers the opposed vices, employing Plato’s and Aristotle’s scheme that the virtues are the habits lying in the mean between too much (excess) and too little (deficit), like proper weight, between corpulence and anexoria, (e.g., II-II 10.5): so justice is giving others what is their due, while profligacy is giving too much, and stinginess is giving less than what is reasonable. And courage is the active propensity to act against obstacles, when reasonably afraid of the danger, while cowardice is loosing action to the fear, and rashness is the tendency to act, underrating the danger.

Aquinas elaborates on whether the defects and excesses are from deficiencies of understanding, weakness of resolution, distraction, and the like. Even the modes of habits are detailed, for example, virtuous anger (in defense of the innocent, or in self-defense), is distinguished from the many sorts that are evil: rage, wrath, ire, revenge, sullenness, indignation, contempt, vindictiveness, and rancor (II-II, 158). For instance, his descriptions of human passions and emotions distinguish feelings, like the “fervor,” “languor” and “melting” effects of love (I-II, 28, 5), and the pleasure, both in presence and in memory, caused by sadness (I-II, 32,4), as well as by rage.

External: The Treatise on Law, I-II, 90-108. Law, both human and divine, is an external explanatory feature of human action because it regulates it. This Treatise is one of the most influential documents in Western Legal History. It is part of Aquinas’ general natural moral law theory, basically that the general principles of morality are known by human understanding and experience of what it is in accord with rightly used reason for a human being to do. There is a basic principle, evident from human nature, “act in accord with reason”. All the rest of the principles are specifications of it, some obvious in themselves and others through experiences.

Theologically, such moral law is a human cognitive participation, in the divine regulation of the universe (Eternal Law, I-II, 93,6, God regulated the universe by divine governance and positive law). That presupposes that all human beings form one real kind of thing that does not vary in essentials with history or environment, race or culture, and is the foundation of universal moral principles.

The very basic moral principles are self-evident, that is, evident just from a consideration of them. However, he acknowledges that the self-evidence of some propositions is accessible only to the educated, (I-II, 94,2). But the most basic “first principles” are obvious to everyone: as “do good and avoid evil”, “act in accord with reason”, “do not do what you believe to be wrong”, “preserve your own life,” “care for human beings”(I-II, 94,2).

There are equally obvious “secondary principles” that fill out and apply the primary ones, like “do not harm others” (I-II, 94,5 ad 3), but involve more particular circumstances, such as the Ten Commandments of Biblical Law (I-II, 100), prohibiting idolatry, murder, rape, torture, theft, and commanding worship of God and respect for parents. They belong to the natural moral law as well as to divine positive law (the revealed Commandments).


Then for circumstances more complex, more qualified, but still general, other principles are required by reason, such as “help the afflicted”, “educate your children”, “return things left with you for safe-keeping”, “pay back what you borrow”, that are subject to particular qualifying conditions or conditions of application that vary and can’t be settled by a list of exceptions in advance of cases, e.g. “ but you don’t give weapons back to a now mad-man., …and so on”.

And then there are even more particular, but general rules, like ‘care for your parents’, ‘get medical care for sick children’ that have qualifications, as reason accommodates to one’s particular situation. He says, “in matters of action, truth or practical rectitude is not the same for all as to matters of detail, but only as to general principles; and where there is some rectitude in matters of detail it is not equally known to all.”(I-II, 94,4). So it might not be surprising that, unless one were specially trained, one might not know what reason requires in the way of transferring real property to another, or how to care for the dying or how to relieve pain, or whether a lawyer can present a witness he knows will lie, what punishments are fitting for offenses, and how such ideas are conditioned by local custom that can amount to law (I-II, 97,3).

So he claims there are simple, obvious, absolutely certain, unchanging moral principles for all times and circumstances that are the bedrock of morality, but that the more particular principles become, the less certain and the less universal they may be, depending on various factors, as do the usages of war, on the customs and abilities of times, persons, and places, and, when proportionality or special sorts of issues (I-II, 95,4) are involved (see below), they may be subject to uncertainty and variability.

Thus, the widespread picture of his natural law moral theory as conservative, static, authoritarian, and a priori, distorts it. For it is empirical, adaptive, and, when applied to civil law, is the origin of the fist general account of the invalidity of legislation, and of insuperable rights of conscience against the state. It even has revolutionary consequences, as when Aquinas argues, II-II-66, 7, “Hence whatever certain people have in superabundance is due by natural law to the purpose of succoring the poor--” and, in some cases may be taken away by force. He also speaks of “things which are of human right” (ibid), e.g., by law, as being subordinate to the natural and divine law: “that man’s needs have to be remedied by those very things” that someone else claims are his.

Moreover, natural law can change by accretion and adaptation (I-II, 95,5 and 97-104). The primary and very general secondary principles do not change. But the content of natural moral law, both requiring and prohibiting things, can grow as circumstances change, and some requirements may not continue for every case, as when there are special causes hindering the observance of such precepts (e.g., the despotic suppression of religion might abate the requirement of public worship for a time). He does not discuss whether something thought permissible in the past maybe found, in new circumstances, impermissible (e.g. executions, or slavery), or something previously thought contrary to reason, may later be found to be required by reason, say, equal political status for all the governed, or population control over the whole earth. But it seems that his moral theory requires both changes by contraction and expansion. For what reason requires and prohibits is a function human nature and the conditions of human life, mediated by human experience.

Foundations of civil law. Aquinas’s overall scheme is that the main fabric of civil and criminal law (and of the judicial system), is an application and particularization of natural moral law.

He observes that society is cooperative, and aimed at things that are important goods for everyone that cannot be reliably achieved by mere cooperation, without entrusting, what otherwise would be individual rights of defense and coercion, to a common source. So, government is coercive power (i.e., for taxation, war, police, and regulated commerce) toward the common good of everyone (e.g., II-II-66 8), under public rules that must meet certain conditions to be civil law, and thus morally as well as effectively binding upon everyone.

Aquinas derives the justified coercive power and existence of the public legal institutions of both civil and criminal law from the consent of the governed; that is, from a people’s grant, directly or indirectly by custom, of what would otherwise be inefficient, and perhaps excessive, individual coercive power, to a ruler for their common well being. In fact law is defined as:

“ regulation (ordinatio) in accord with right reason, by the one charged with care of the community [ruler], aimed at the common good and promulgated” (I-II, 90,4).

“Coercively” is implicit in “regulation”. The definition specifically requires (1) jurisdiction (both personal and over subject matter), “charged with ..”; (2) a public objective, “aimed at the common good”, not private enrichment or privilege of the few or the rulers;(3) in accord with right reason: nowadays phased: ‘reasonably related to legitimate public objective’; and (4) promulgated: that regulations be made known to those governed (no secret or ex post facto laws).

In the absence of any of those conditions, a general command is not law: it is void. Historically, that is the first general philosophical theory of the invalidity of legislative enactment.

Aquinas identifies further conditions of legislative invalidity: acts “beyond the power committed to the legislator”; burdensome schemes of unjust enrichment, “directed to the cupidity and vainglory of rulers”(I-II, 94,4), and schemes so burdensome as to destroy the common good (e.g., individual expression); and unequal burdens imposed, even for legitimate public aims, upon the community (equal protection under law) (I-II, 95,2). “The like are acts of violence rather than laws” (I-II, 96,4). Those criteria have survived into the body of current American, and many other nations’ Constitutional law.


Moreover, legislative power does not extend to prohibit private vices, or intentions, or inner vices (I-II, 96,2), only public ones affecting others; or allow the law to require all virtues, even useful ones, unless needed for the common good (I-II, 96,3).

And the law may be disobeyed, morally, when the burden is imposed unequally on the community, unless the danger of scandal forbids it. And, of course, enactments contrary to divine law “are in nowise to be obeyed”. “Law that conflicts with the law of nature is no longer a law but a perversion of law” ((I-II, 95,2).

Disobedience is also permitted in a variety of circumstances, for instance when reasonable disregard of the letter of the law is needed to attain the very purpose of the law (e.g., public safety) (I-II, 96,6), but with limitations (ibid, ad, 2 and 3); and when there are special dispensations that are permitted by law, and when there are differences of legitimate status under law (I-II, 98,4, ad 2).

The basic scheme of justified civil legislation is application of natural moral law to public acts for public objectives, by what he calls (i) “conclusions of natural law”, with extensive (ii) “determinations” settling what is indeterminate in moral law, but needed for an orderly body of law. So if natural morality requires (as a conclusion from “do not harm others”) building codes for public safety, then the particular standards, that could reasonably be different, are “determinations” within the wisdom and discretion of legislators. The same would apply to traffic patterns, zoning laws, tax codes, trade regulations, food safety and thousands of others elements of public safety and convenience and commerce, though the legal systems of his time were much simpler; and he might generally be found on the side of legislative minimalists; for he also proposed that persons harmed by changes of law for the better should be compensated (I-II, 97,2).

He briefly sketches “law of nations” (jus gentium), combining some principles of natural law (e.g., for just payments for trade) and some agreements by sovereigns, that, (I-II, 95,4), anchored in the Roman tradition of law for the provinces and conquered people, became the schema of 16th Century and later theories of International Law. He says that such law, even though “natural to man” is nevertheless distinct from natural law (I, 95.4 ad 1), mainly because it is sketchy, and by agreement of sovereigns.

He offers a theory of just war (II-II, 40) on principles of self-defense, (which implies the principles of revolution and rebellion, as well), and of civil disobedience, partly to be found in the conditions stated (I-II 96,4 and 6) and by analogy from the principles of conflict. The basic principles of those theories are (i) proper public authority to act;(ii) moral necessity to act against a wrongdoer or aggressor, (iii) a permissible intention (e.g., not just vengeance) and reasonable prospect of success, (iv) proportionality (e.g., I-II, 95, 2 and 96,6) in the losses in relation to the gains, and (v) only incidental and not great harm to non-participants (not disproportionate collateral damage); and (vi) no targeting or aimed injuring of the innocent (in a word, no terrorism). The latter provisions (iv and v, vi) have been culled by commentators from other places in his moral theory, and from his other writings. These ideas have reverberated in legal systems ever since. So too have the Questions, II-II 67-71, on judges, prosecution and accusation, defense, witnesses and counsel in judicial proceedings.

Aquinas did not offer a theory of individual human “demand rights” against government; his was a theory of the nature and limitation of public legislative coercion against the governed, with some development of the moral right to resistant, disobedient and interpretative (I-II, 97,6 ad 2 and 3) acts. Individual rights theories came later.

Finally, Aquinas, like Augustine, regarded civil law as a necessity arising from the sinful condition of mankind in which conflicts and crimes arise. All such coercive law will by abrogated as unnecessary with the establishment of the Kingdom of God. From the principles of natural philosophy, Aquinas speculated but did not attempt to prove, that the sun will die and the stars go out, and the earth will be destroyed, but “the substance of the creation will endure forever”, and on religious grounds he affirmed that all humans will be resurrected and be finally judged and granted everlasting happiness in life with God, or condemned in everlasting rejection and separation from God.

Overall. The work is dominated and organized by the task of providing a unified conception of the origin and destiny of the world, and of individual life, within the framework of the Catholic Christian Faith. The philosophical underpinning of it all, and the detailed explanation of the religion in a unified philosophical system and with explicit philosophical reasoning, distinguished this book from any prior comprehensive Christian work; and its excellence as philosophical craftsmanship established it as one of the classics of the history of philosophy and one of the most influential works of Western Literature.

Select Bibliography.

Primary Sources:

Thomas Aquinas. Sancti Thomae de Aquino Opera Omnia, Leonine Edition, Rome (1882--.), Vols. 4-12: Summa Theologiae.

Summa Theologiae, Blackfriars Edition, Latin and English, with notes and introductions, 61 volumes, 1964-80

The Summa Theologica of Saint Thomas Aquinas, translated by the Fathers of the English Dominican Province (1946), in 5 vols. (Paperbound.Christian Classics). Available on Web at :

Summa Theologiae: a concise translation, 651 pp, selected, translated and edited by Timothy McDermott. (1989).

Secondary Sources in English:

Anscombe, G. E. M., Ethics, Religion and Politics (1982).

` And P. T. Geach, Three Philosophers(1961).

Copleston, Frederick, History of Philosophy (9 vols.): Medieval Philosophy, Vol. II, Augustine to Scotus (1993).

Davies, Brian, The Thought of Saint Thomas Aquinas (1992).

Gilson, Etienne, The Christian Philosophy of Saint Thomas Aquinas (1957).

A History of Christian Philosophy in the Middle Ages (1953).

Henle, R.J., Saint Thomas and Platonism (1956).

Kenny, A., Aquinas on the Mind (1993).

Aquinas (1980).

Kretzmann, N and Stump, E., eds, The Cambridge Companion to Aquinas (1993).

Lysska, A., Aquinas’s Theory of Natural Law (1996).

Lyttkens, H., The Analogy Between God and the World,( 1952)

MacIntyre, A. Three Rival Versions of Moral Inquiry (1990).

Sillem E., Ways of Thinking About God (1960)
Torrell, J-P, Saint Thomas Aquinas, The Person and His Work , I. (1996).

‘ Weisheipel, J., Friar Thomas d’Aquino, His Life, Thought and Work,( 1974, rev. 1983).

Wippel, J., The Metaphysical Thought of Thomas Aquinas, (2000).

Metaphysical Themes in Thomas Aquinas, (1984).