METAPHYSICS the developments of the Theory of Forms in the Parmenides and the Sophist He does, however, often tacitly make use of Plato’s later thoughts in his own writings, in particular when developing his own theory of forms in Metaphysics F There, he treats on equal terms problems with Plato’s theory and diYculties in his own The book is dense and diYcult, and the account of it I now give can only claim to be one possible thread to guide us through its labyrinth The diVerence between Aristotelian forms and Platonic Forms is that for Aristotle forms are not separate (chorista): any form is the form of some actual individual As we have seen in our account of Aristotelian physics, form is paired with matter, and the paradigm examples of forms are the substantial or accidental forms of material substances Aristotle cannot avoid, however, the questions for which Plato sought a solution in his theory He must, for instance, provide his own answer to someone who asks what is common to the many things that are called by the same name or fall under the same predicate He must, that is, oVer an account of universal terms In Metaphysics F Aristotle discusses the relationships between being, substance, matter, and form He there works to relate the teaching of the Categories on substance and predication with the teaching of the Physics on matter and form, and he combines the two together, with modiWcation and ampliWcation, into a treatise on Being ‘The question that was asked of old, and is asked now, and always will be asked and always will be a problem is ‘‘what is Being?’’ And this is the question; ‘‘what is substance?’’ ’ (F 1028b2–4) The reason he gives for eliding the two questions recalls the Categories Whatever there is must be either a substance or something that belongs to a substance, such as a quantity or a quality of it When we are listing the things that there are, we may count, if you like, health and goodness; but any actual health is someone’s health, and any actual goodness is the goodness of something or other If we ask, in such cases, what really and truly is, the answer will be: this healthy person, this good dog (F 1028a24–30) So Aristotle can regard it as obvious that material entities like animals and plants and earth and water and the sun and the stars are substances (D 1017b8; F 1028b8) He puts on one side, for later treatment that we have no space to follow, a number of further questions Are surfaces, lines, and 217