 If there is a feature of Aristotle’s thought that casts doubt on his empiricism, it is the account of scientific reasoning found in his Posterior Analytics. That account is deductive: it involves a derivation of the fact to be explained from first principles, the latter being “true, primary, immediate, better known than and prior to the conclusion, the latter being related to them as effect to cause” (APo. 71b20–24). There has been much debate regarding the role of such demonstrations. But the most plausible view is that they are not, for Aristotle, a means of making scientific discoveries; they are the way in which such discoveries should be presented (Barnes 1994, xii). Indeed Aristotle expressly denies we can discover explanatory principles by way of demonstration, holding that such demonstrations serve merely to make them clear (APo. 93b16–18). This view seems consistent with Aristotle’s practice in his own scientific writings, as well as the methodological remarks found in his biological works. He argues, for instance, that when studying animals “we ought first to take the phenomena that are observed in each group, and then go on to state their causes” (PA 640a15). While we should not confuse Aristotle’s empiricism with that of Francis Bacon (Harari 2004: 35), even his theorizing can be said to begin with what is observed.