The more scientifically educated the Greeks became, the more complex their interpretations of dreams were.  In contrasting Homer's Iliad and his Odyssey with Aristotle's "On Dreams", one can see the scientific difference.  Homer's interpretations of dreams were very simple and straightforward, whereas Aristotle's were very complicated:  he showed that he was uncertain of many things having to do with the interpretation of dreams.  Homer innocently believed that the gods were in control of all dreams, but Aristotle was divided between whether dreams were from solely sensory impressions or whether the gods did have some control.  Homer preferred fancy and idealism, whereas Aristotle was logical and reasonable.  Perhaps therein lay his complexity.
         Homer was a firm believer in the old Greek way of interpreting or explaining dreams.   This interpretation held that all dreams were from the gods and that true dreams came only to the most important of people.  This view was relatively simple to understand; it was very straightforward.  Homer was a poet, and a great one historically and due to the literary value of his works, yet he was not a scientist, nor even a philosopher.  He did not consider things fundamentally from a scientific method, or even with logic.  His forte was simply entertainment and history:  usually his purpose fell somewhere between achieving both.  In his Iliad, Homer wrote of a dream that Agamemnon, the Greek king, has concerning making war with the Trojans.  This dream was sent from Zeus, and it was a false dream telling Agamemnon to lead the Greeks into war against the Trojans.  (Homer, Iliad, p.20-1.)  Homer personified the dream as one subordinate to Zeus:  "And to it he spoke these feathery words: / 'Go, deadly Dream, along the Greek ships...'"  (Homer, Iliad, p.20.)  Zeus thus addressed the Dream and "The Dream listened and went... / The Dream stood above his head..."  (Homer, Iliad, p.20-1.)  The Dream was clearly a divine representation; it was a manifestation of the god's wishes.  Also, the Greek soldiers did not doubt the dream because it came to Agamemnon and he was the king.  (Homer, Iliad, p.22.)  Dreams only truly came to very important people:  "If any other man told us this dream / we would call it a lie and turn our backs on him."  (Homer, Iliad, p.22.)  Homer here depicted the older, nonscientific Greek interpretation of dreams, in which he was a firm believer.
        Somewhere between Homer and Aristotle, the Greeks started to have literature written by men of science and philosophy.  Aristotle's teacher, Plato, and Plato's teacher, Socrates, were among the first of these logical men.  These men started to want other methods of explaining phenomena other than by the various facets of the gods; they search for scientific explanations for everything, including dreams.  Where the gods were clear-cut about dreams, science was not so accommodating.  Logic made things much more complicated.  Aristotle, in particular, was confused about where dreams originated.  His scientific thought processes led him to believe that dreams came from sensory impressions that the brain accumulated during the day.  (Aristotle, "On Dreams", p.622.)  However, Aristotle struggles with the gods' involvement in dreams.  At first he states that the sender of dreams cannot be god as the receiver is just commonplace man and divination has little connection with dreams  (Aristotle, "On Prophesying by Dreams", p.626.)  Then he avers dreams have a divine aspect; "for Nature is divinely planned, though not divine itself."  (Aristotle, "On Prophesying by Dreams", p.628.)  In this, Aristotle reflected his Greek tutelage:   the gods only give true dreams to the important, so then dreams must not come from the gods, since lower people also receive them.  It is interesting to note that Aristotle realized what Homer did not:  common people also have dreams.  Aristotle also held a deep belief that dreams were purely coincidental to the sensory impressions of that particular day, but he also gave credence to a conflicting idea of Democritus.  (Aristotle, "Prophesying by Dreams", p.628-9.)  Democritus believed that images and emanations cause dreams, "since persons are more sensitive even to slight sensory movement when asleep than when awake", and these movements of the emanations cause the presentations of the dreams, which are predictive of the future.  (Aristotle, "Prophesying by Dreams", p.628-9.)  Aristotle spends so much time on this theory that one would suppose that he thought it was a legitimate theory on dreams.  Aristotle threw many possible theories and interpretations up into the air; he was obviously not  completely convinced on any of the theories.  The essence of the scientific process is that one experiments over and over again; one experiment is not enough to form a scientific law.  Aristotle would tie himself down to any one "law"; he would try out many different possibilities and see which was the best fit.
         The contrast between Homer's Iliad and Aristotle's "On Dreams" and "Prophesying by Dreams" depicts the slow scientific progression of  the learned men of ancient Greece.  Homer believed that  the gods were in control of dreams.  It was as simple as that because Homer was a poet, not a scientific thinker like Aristotle.  Aristotle did not think gods controlled dreams, but there was a divine aspect to dreams.  And dreams were pure coincidence, but Democritus' theory of emanations might have some legitimacy in predicting the future.  Aristotle was very ambiguous and confused in reference to dreams and dream origins.  Perhaps thinking gets in the way of the divine and manages to confuse things.  After all, the well-educated tend to want to analyze and explore things, whereas the uneducated tend to accept things at face value.  This may explain why Homer, the scientifically uneducated, had a simple explanation for dreams, and Aristotle, the scientifically learned, had a complicated jumble of ideas.  For it is certain that, as the Greeks gained more scientific knowledge, their ideas on dreams became infinitely more intricate.