The maxim of quality, where one tries to be truthful, and does not give information that is false or that is not supported by evidence.
As the maxims stand, there may be an overlap, as regards the length of what one says, between the maxims of quantity and manner; this overlap can be explained (partially if not entirely) by thinking of the maxim of quantity (artificial though this approach may be) in terms of units of information. In other words, if the listener needs, let us say, five units of information from the speaker, but gets less, or more than the expected number, then the speaker is breaking the maxim of quantity. However, if the speaker gives the five required units of information, but is either too curt or long-winded in conveying them to the listener, then the maxim of manner is broken. The dividing line however, may be rather thin or unclear, and there are times when we may say that both the maxims of quantity and quality are broken by the same factors.