A longstanding problem concerning Aristotle's philosophy of science is the extent to which there is a serious conflict between the account of scientific explanation and investigation in the Posterior Analytics and the explanations and investigations reported in treatises such as the Historia Animalium, Parts of Animals, and Generation of Animals. I shall not here mount a frontal attack on this question, preferring instead a rearguard action. This will consist of (i) articulating a familiar epistemological distinction between unqualified and sophistic or incidental understanding, which plays a fundamental role in Aristotle's philosophy of science; (ii) relating that distinction to the methodological recommendations of Posterior Analytics 11.14; and (iii) presenting three sorts of evidence from the PA and HA indicating that the zoological works owe a great deal both to the above epistemological distinction and to its methodological implications. The evidence for (iii) will consist of the organization of information found in the HA, the relevance of that organization to the explanations of PA, and the theoretical and practical concern with the way in which lack of an appropriate zoological nomenclature can hamper the achievement of understanding. The evidence points to a much more direct relationship between the APo. and the biology than recent commentators have suggested.