In Chapter 9, I argue that, in DA 1.5, Aristotle sums up the basic shortcomings of early Greek psychology by arguing that these theories are at best able to provide an explanation of either the soul’s power of perception, or its power to initiate the body’s local motion, but not both. This criticism lays out the empirical groundwork for Aristotle’s claim in DA 2.3 that there is no uniform entity called ‘soul’ in nature, but various kinds of soul associated with broad divisions in the animal kingdom. I argue that this discussion places a negative constraint on him to adopt the Non-Uniformity Thesis.