 What, then, does PA I tell us about the proper way to investigate animals? Aristotle begins by posing a problem about how to identify the proper objects of investigation. Should we begin by studying the features of groups close to the level of perception, such as human beings, horses, dogs and such, or should we look for attributes that ‘belong in common according to kind, and then later study their distinctive attributes’ (639b4–5). He notes that since there are many attributes that are common to many of these more concrete kinds, focusing our study on them will have the result of our repeating ourselves—much as if, to use an example from APo II discussed in Section 2, we were to remain at the level of ‘olive trees lose their leaves’, ‘grape vines lose their leaves’. Among these common attributes, Aristotle distinguishes those that seem not to differ across the kinds that have them (he cites respiration and death) from those that are ‘ distinctive in form ’ such as locomotion. As he puts it: “it is apparent that locomotion is not one in form, because flying, swimming, walking, and crawling differ” (639b1–2). Aristotle deals with this question, so reminiscent of APo. I 4–5, in PA I 4, but only after he has introduced a new way of thinking about differentiae and division appropriate for investigating animals. After discussing his recommendations regarding the use of logical division in biology, we will return to look at his answer.