The range of Aristotle's investigations in zoology is such that a discussion of his use of empirical methods has to be drastically selective. Yet the need to come to some assessment of his performance in this field is all the more pressing in that it has been subject to such divergent judgments. Some of the most extravagant praise, but also some of the most damning criticisms, have been directed at his empirical researches in zoology.

The massive array of information set out in the main zoological treatises can hardly fail to impress at the very least as a formidable piece of organization. But both Aristotle's sources and his principles of selection raise problems. As we have already noted in connection with his use of dissection, it is often impossible to distinguish Aristotle's personal investigations from those of his assistants, although, given the collaborative nature of the work of the Lyceum, that point is not a fundamental one. It is abundantly clear from repeated references in the text that he and his helpers consulted hunters, fishermen, horse-rearers, pig-breeders, bee-keepers, eel-breeders, doctors, veterinary surgeons, midwives and many others with specialized knowledge of animals. But a second major source of information is what he has read, ranging from Homer and other poets, through Ctesias and Herodotus to many of the Hippocratic authors. In general he is cautious in his evaluations of all this secondary evidence.