A major feature of Aristotle's strategy against Plato in the Categories is to collapse the dichotomy that Plato's theory of (metaphysical) predication attempts to make between forms and sensibles. In Aristotle's theory, Socrates IS some of his predicables, but HAS others. He IS what is essential to him, and HAS the rest. These different relations between Socrates and his various predicables form a large part of the motivation for the further ontological distinctions that Aristotle draws in the Categories.
Lewis, Frank A., "Substances, Accidents, and Kinds: Some Remarks on Aristotle's Theory of Predication" (1984). The Society for Ancient Greek Philosophy Newsletter. 108.