This paper discusses the relation between νοῦς (the knowledge of scientific principles) and ἐπιστήμη ἀποδεικτική (the knowledge of demonstrable truths) in Aristotle's philosophy of science. I argue against "rationalist" interpretations, dominant in the secondary literature, which claim that the principles can be known as such independently of their causal connections to demonstrable truths. However, alternative interpretations imply that νοῦς and ἐπιστήμη ἀποδεικτική are somehow interdependent, a view that seems in conflict with the fact that νοῦς is, according to Aristotle, more "accurate" than ἐπιστήμη ἀποδεικτική. Thus, I offer a construal of the relation between these two cognitive states and explain in which sense they can be taken as interdependent without contradicting Aristotle's claim about their "accuracy" or rendering his theory viciously circular.keywords Aristotle, demonstration, knowledge, science 1 . i n t r o d u c t i o n according to aristotle's posterior analytics (hereafter, An. Post.), scientific expertise is composed of two different cognitive dispositions. Some propositions in the domain can be scientifically explained, which means that they are known by "demonstration" (ἀπόδειξις), a deductive argument in which the premises are explanatory of the conclusion. Thus, the kind of cognition that apprehends those propositions is called "demonstrative knowledge" (ἐπιστήμη ἀποδεικτική). 1 However, not all propositions in a scientific domain are demonstrable. Demonstrations are ultimately based on indemonstrable principles, whose knowledge is called 1 Myles Burnyeat, "Aristotle on Understanding Knowledge," argues that the term ἐπιστήμη is better translated as "understanding." I accept most of the reasons Burnyeat sets out in favor of this translation, but I agree with David Bronstein, Knowledge and Learning, 18-20, that we must emphasize that ἐπιστήμη is a kind of knowledge (the kind of knowledge expert scientists have). Thus, I shall translate ἐπιστήμη as "scientific knowledge" and ἐπιστήμη ἀποδεικτική as "demonstrative knowledge." See James H. Lesher, "On Aristotelian ἐπιστήμη as 'Understanding,'" for a more detailed discussion.