Aristotle

“ Since the demonstrations rest on the universal, and universals cannot be perceived by the senses, it is clear that one cannot acquire scientific knowledge by means of sense perception. Even if we could have perceived that a triangle has its angles equal to two right angles, we should certainly have gone on to search for a demonstration of it, and should not, as some assert, have already known the fact by means of perception alone. Perception as an act must deal with the particular alone, while scientific knowledge consists in learning the universal. ”

“ I do not deny that after seeing the same phenomenon occur repeatedly we might search out the universal law, and thus attain to demonstration, seeing that knowledge of the universal results from repeated acts of sense perception. But the value of the universal lies in its shewing the cause of particular phenomena, and consequently the universal is more important than the perception of particular cases or the immediate apprehension of such things as have for cause something other than themselves. ”

“ If we saw that the burning-glass was porous and that the light filtered through the apertures, it would be clear why it burns, because we should see the phenomenon occur in every separate glass; but we should yet have to form the abstract idea that this quality is universally true of every possible glass. ”