Aristotle claimed that he did not understand Plato's concept of "participation." (When a philosopher claims "not to understand" something, it means that he is pushing for a better account of it, that he is not at all satisfied so far.
Aristotle probably understood Plato as well as anybody ever has.) Aristotle's objection was, essentially, that Plato had failed to explain the relationship between the Forms and particular things, and that the word "participation" was no more than "a mere empty phrase and a poetic metaphor."
Furthermore, Plato's emphasis on the Forms made it impossible to appreciate the full reality of particular things, and the eternal permanence of the Forms made them useless for understanding how particular things could change. Indeed, the question "How do things change?" becomes the central theme of Aristotle's philosophy.
Aristotle also wanted to determine the nature of reality. But Plato had argued that reality was some-thing other than the world of our experience. Aristotle, a practical man of the earth, a great biologist, physicist, and worldly tutor to Alexander the Great, would have none of this. This world, our world, is reality. He agreed with Plato that knowledge must be universal and concerned with what things have in common, but he rejected Plato's idea that these common universal ingredients-the Iris of things-could be separated from particular things.
But this meant that Aristotle also rejected Plato's separation of the human soul from the body, and Aristotle, unlike Plato, saw human beings entirely as creatures of nature, "rational animals"-- but still animals. Metaphysics, for Aristotle, was not the study of another world, recollected in our eternal souls; metaphysics was simply the study of nature (physics), and, as importantly, the study of ourselves.
Accordingly, he brought metaphysics back home. But it must not be thought that he made it any simpler. The beginning student of Aristotle as well