  Aristotle did not believe in Platonic Forms, existing independently of their instances. Aristotelian forms (the capital ‘F’ has disappeared with their standing as autonomous entities) are the natures and properties of things and exist embodied in those things. This enabled Aristotle to explain the union of body and soul by saying that the soul is the form of the body. This means that a particular person’s soul is no more than his nature as a human being. Because this seems to make the soul into a property of the body, it led many interpreters, both ancient and modern, to interpret his theory as materialistic. The interpretation of Aristotle’s philosophy of mind – and, indeed, of his whole doctrine of form – remains as live an issue today as it was immediately after his death (Robinson 1983 and 1991; Nussbaum 1984; Rorty and Nussbaum, eds, 1992). Nevertheless, the text makes it clear that Aristotle believed that the intellect, though part of the soul, differs from other faculties in not having a bodily organ. His argument for this constitutes a more tightly argued case than Plato’s for the immateriality of thought and, hence, for a kind of dualism. He argued that the intellect must be immaterial because if it were material it could not receive all forms. Just as the eye, because of its particular physical nature, is sensitive to light but not to sound, and the ear to sound and not to light, so, if the intellect were in a physical organ it could be sensitive only to a restricted range of physical things; but this is not the case, for we can think about any kind of material object (De Anima III,4; 429a10–b9). As it does not have a material organ, its activity must be essentially immaterial.