 A number of texts in Aristotle’s causal investigations reinforce the message of HA I 6, stressing that the preliminary work of inquiries that establish and organize the facts at various levels of generality has been accomplished; and they regularly refer to something like what is reported in our HA as the place to look for the results of this preliminary work. Two explicit statements to that effect follow, one from the beginning of his study of the causes of the differences in animal locomotion, one from the beginning of his study of the causes of the differences among the parts of animals.