Aristotle held with Plato that we possess a faculty, intellectual intuition, by which we can visualize essences and find out which definition is the correct one, and many modern essentialists have repeated this doctrine. Other philosophers, following Kant, maintain that we do not possess anything of the sort. My opinion is that we can readily admit that we possess something which may be described as ‘intellectual intuition;’ or more precisely, that certain of our intellectual experiences may be thus described. Everybody who ‘understands’ an idea, or a point of view, or an arithmetical method, for instance, multiplication, in the sense that he has ‘got the feel of it,’ might be said to understand that thing intuitively; and there are countless intellectual experiences of that kind. But I would insist, on the other hand, that these experiences, important as they may be for our scientific endeavours, can never serve to establish the truth of any idea or theory, however strongly somebody may feel, intuitively, that it must be true, or that it is ‘self-evident.’ Such intuitions cannot even serve as an argument, although they may encourage us to look for arguments. For somebody else may have just as strong an intuition that the same theory is false. The way of science is paved with discarded theories which were once declared self-evident; Francis Bacon, for example, sneered at those who denied the self-evident truth that the sun and the stars rotated round the earth, which was obviously at rest. Intuition undoubtedly plays a great part in the life of a scientist, just as it does in the life of a poet. It leads him to his discoveries. But it may also lead him to his failures. And it always remains his private affair, as it were. Science does not ask how he has got his ideas, it is only interested in arguments that can be tested by everybody.
From The Open Society and its Enemies Volume 2. Princeton University Press 1966