Aristotelian commenters have long noted an apparent contradiction between what Aristotle says in Posterior Analytics I.2 and Physics I.1 about how we obtain first principles of a science. At Posterior 71b35–72a6, Aristotle states that what is most universal (καθόλου) is better-known by nature and initially less-known to us, while the particular (καθ’ ἕκαστον) is initially better-known to us, but less-known by nature. At Physics 184a21-30, however, Aristotle states that we move from what is better-known to us, which is universal (καθόλου), (...) to what is better-known absolutely, which is particular (καθ’ ἕκαστον). This paper turns to two of Aristotle’s most notable medieval commentators—Albertus Magnus and Thomas Aquinas—to resolve this apparent contradiction. The key to Thomas and Albert’s solutions, we will argue, is a twofold distinction between a sense-perceptive and scientific universal, and the particulars as sensed individuals and as differentiating attributes. Our Synthetic treatment of these distinctions contributes to the ongoing scholarly effort to understand the Stagyrite’s complex theory of knowledge. (shrink)