In the Nicomachean Ethics (NE), Aristotle argues by a process of exhaustive enumeration that the virtues of character are hexeis. The Metaphysics account says that the thing which has a hexis is well or ill disposed. Aristotle's claim in NE that virtues of character are hexeis, then, depends upon the eminently reasonable assumption that people have characters which are complex and which have the good or bad features which they do in virtue of their parts being arranged in a particular way. Qualifications cover a very extensive territory, therefore; colour, temperature, smell, taste, density, kinds of functioning, and evaluative categories of all sorts are all respects in which a thing could change kata poion. Aristotle thought that his biology was a scientific advance on that of his predecessors in virtue of possessing more explanatory power. Aristotle is concerned to prove that the only subjects of alteration are those things that are involved in perceptual interaction.