In fragments of the lost Protrepticus, preserved in Iamblichus, Aristotle responds to Isocrates’ worries about the excessive demandingness of theoretical philosophy. Contrary to Isocrates, Aristotle holds that such philosophy is generally feasible for human beings. In defense of this claim, Aristotle offers the progress argument, which appeals to early Greek philosophers’ rapid success in attaining exact understanding. In this paper, I explore and evaluate this argument. After making clarificatory exegetical points, I examine the argument’s premises in light of pressing worries (...) that the argument reasonably faces in its immediate intellectual context, the dispute between Isocrates and Aristotle. I also relate the argument to modern concerns about philosophical progress. I contend that the argument withstands these worries, and thereby constitutes a reasonable Aristotelian response to the Isocratean challenge. (shrink)