In the first half of APo. A 13, Aristotle introduces the distinction between the knowledge of a fact and the knowledge of the reason why within the same science. These two levels of knowledge are deductively structured. On the basis of the choice of middle term we can identify the deduction of the reason why and at least five kinds of the deduction of the fact. A central interpretive question concerns the function that the knowledge of the fact plays in scientific process. The deductions of a fact seem to characterize the first stage in the investigation into the reason of a property; they are not opposed to demonstration. For example, the deductions that proceed through the more familiar of the convertible terms discover less familiar properties and bring about the contents of the deductions of the reason why. Consequently, the knowledge of the fact finds the items whereon the knowledge of the reason why is grounded.
Keywords: Posterior Analytics, science, demonstration, reason why, deduction