SENECA; Davie, John; Reinhardt, Tobias (2007-10-11). Dialogues and Essays (Oxford World’s Classics) . Oxford University Press. Kindle Edition.
Epistemology, or the theory of knowledge, is integral to Stoic ethics. For virtuous behaviour as characterized above to be possible, human beings must not hold any beliefs which are false, for if they did it might be possible for these false beliefs to form the premises of arguments which lead to the conclusion that another, true belief is false; clearly this cannot be allowed to happen, which is why the sage only holds true beliefs. The Stoics agree again with Socrates that, if we want to have a really good life—a life of the sort that human beings are programmed and constructed to have—we have to have knowledge of certain facts, in the first instance of the world around us; we need to be sure that what we think we know we really do know; and we need to have a theory which explains how all this is possible. Now the Stoics distinguished between opinion, a variable epistemic state characteristic of human beings who are not sages, and knowledge, which only the sage (and the supremely rational being that is god) possesses. Between these two states they recognized a third, cognition (katalêpsis), which is different from opinion in that it is guaranteed to be true, and different from knowledge in that one can theoretically still be argued out of it (that to know something amounts to holding that something is the case, and to be so firm in that view that one cannot be reasoned out of it, is also already a Platonic position). Crucially, cognition is a state that is available both to the sage and the non-sage, and hence represents the pivotal route by which someone who is aspiring to become rational and virtuous can become so.”