This paper offers a novel interpretation of the nature and role of logical argumentation in Aristotle’s natural philosophy. In contrast to the standard domain interpretation, which makes logikôs argumentation the contrary of phusikôs, relying on principles drawn from outside the domain of natural science, I propose that the essential or defining feature of logikôs argumentation is the use of principles that are general relative to the question under investigation. My interpretation is developed and illustrated with a close textual analysis of (...) Aristotle’s explanation of mule sterility in Generation of Animals II 8. (shrink)