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Aristotle (384–322 B.C.E.) has comparatively little to say directly about knowledge. But it is clear that he too conceives of knowledge as involving systematic understanding. The findings of a properly developed science, he thinks, can ideally be laid out in connected sequences of explanations. The starting points are the natures or essences of the objects being studied—say, the essence of a cow; these natures or essences explain why the objects have certain features, which in turn explain why they have certain other features, and so on. Aristotle's remarks on how we come to know the starting points are somewhat baffling. What is clear is that sense perception is a crucial ingredient in the process of coming to know, but that sense perception by itself does not constitute knowledge. This is because sense perception shows us only particular objects; genuine knowledge is by definition about universal characteristics of things. One thus needs to be able to grasp the universal characteristics present in a body of related sensory information. Aristotle shows no lack of confidence in the ability of human beings to do this reliably. But this is no surprise; it is clear that he conceives of the world as ordered in such a way as to be understandable, and of human beings as having the capacities necessary to achieve that understanding—most notably, rationality. However, he stresses, particularly in his ethical works, that one cannot expect complete precision in all subjects; the study of ethics, no matter how expertly conducted, is bound to yield conclusions less exact and more subject to exceptions than the study of mathematics.


We think we know a thing without qualification … whenever we think we know the explanation because of which the thing is so, know that it is the explanation of that thing, and know that it does not admit of being otherwise.

SOURCE: Aristotle, Posterior Analytics, 71b9–12. In Aristotle: Selections, trans. Terence Irwin and Gail Fine.

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Science EncyclopediaScience & Philosophy: Ephemeris to Evolution - Historical BackgroundEpistemology - Ancient - Pre-socratic Philosophy, Socrates And Plato, Aristotle, Hellenistic Theories, Bibliography