Aristotle

“ Thus, if the subject be a bird, we should find the qualities possessed by every bird, and we must continue thus with the attributes of each lower term in the series. We shall then clearly be able to give the reason why the species included in the common genus possess such and such attributes; e.g. the reason why Man or Horse, as species of Animal, possess particular attributes. Let A be animal, B the attributes of every animal, C, D, E, particular species of animal. Now it is clear why B is an attribute of D, namely because of A, and it will similarly belong to the other species of animal. ”

“ Hitherto we have spoken of cases where custom has sanctioned the application of the common class names to the particular species, but we should not limit ourselves to these. If anything else be seen to be an attribute of several things but to have no common generic name, we should take it for examination and look what are its attributes or of what it is an attribute. ”

“ No single designation for instance exists for the spine of a fish, the pounce of a cuttle and ordinary bone, and yet all these parts have common qualities, as if their nature were the same in each case. ”