A basic comparison between the thought of Plato and Aristotle, in similarity and difference.

“Now for such general conceptions as that of manhood, or triangular shape, or any other abstraction that exists in a number of concrete things but nowhere by itself, Aristotle usually adopts the same word that Plato had used for his self-existing realities, namely “kind” or “kinds.” But just as Plato, in addition to this term which he shares with Aristotle, had a synonym which is peculiar to himself, namely “idea,” so Aristotle too has his own special synonym, namely “form.” And in expounding the doctrines of the two philosophers it has, very naturally, been usual to avoid the term “kind” common to them both, and to adopt for each the synonymous term characteristic of himself. Thus we speak of Platonic “ideas” and Aristotelian “forms.” It is a practice which has an undoubted convenience and is conducive to clearness from one point of view, but it has the great disadvantage of always suggesting the difference between the two thinkers and never their common ground, and also of severing the technical language of both of them, from the common matrix of natural, and naturally significant, phraseology out of which it grows and with which it always remains in connection. It is easy, however, to discern this common ground. “Idea” and “form” are mere variants on “kind.” And Plato and Aristotle both investigate such problems as these: What is meant by saying Socrates and Sophroniscus are both “men”? What does it really tell you of them? What does it enable you to understand? When you ask “what” a thing is and get your answer:–It is a cart, a horse, a tree–what really is that “whatness” or “thatness” that makes it the thing it is and not some other thing? And why can you never give any explanation of a thing except by determining some “kind” or “kinds” which it is or to which it belongs? But Plato is always trying to get at something behind the concrete and Aristotle to get at something in it. The Platonic “kinds” or ideas  exist apart from individual things and are the perfect prototypes of which they are the imperfect imitations or reflections; the Aristotelian  “kinds” or forms are abstractions of the human mind that have no actual existence except in transient and concrete individuals.” (Philip H. Wicksteed, Dante and Aquinas, pps 18-19 [bold emphasis mine]).