 This sketch of their implications explains why Philo’s innovations were decisive enough to startle his contemporaries and, eventually, to lead to the doxographical classification of his version of Academicism as a distinct “Fourth Academy” (see, e.g., Sextus PH 1.220 &amp; 1.235). But two facts imply that his further elucidation in the Roman Books included some significant limitations on the range of knowledge Philo came to accept, and hence the sense in which he rejected the skepticism of his Academic predecessors. The first is just that his contemporaries (and later historians) continued to regard him, even at the end of his career, as an Academic, i.e., in some way a follower of Arcesilaus and Carneades, rather than a defector like Antiochus or Aenesidemus. The second is that Philo asserted “the unity of the Academy” in the Roman Books (see Cicero Ac. 1.13), i.e., claimed that his new view was in fact the underlying view of all the Academics from Socrates and Plato to himself. Exactly what he meant by this claim is controversial, but the tenuous and complex evidence does not suggest that it involved either accepting an anti-skeptical reading of Plato or denying that the skeptical Academics were skeptical about the possibility of achieving theoretical knowledge in philosophy (see Brittain 2001: chs. 4–5 and Tarrant 2018: 86–87).