  Philo’s Roman innovation, then, was to reject the Stoic account of knowledge while continuing to accept his predecessors’ arguments that the requirement that cognitive impressions be set apart from other impressions by a special character cannot be satisfied (cf. Barnes 1989, 70–76).  For there to be knowledge, he now held, it was enough that there be impressions which are true and accurately formed (Cicero Acad. 2.18). It is not hard to see why Antiochus was disturbed, for, if this is right, Philo was the legitimate heir of a single unbroken Academic tradition stretching back to Plato in which there was no place for alien Stoic doctrines. Cicero, who is our principal source, chose not to recount the details of this controversy (Acad. 2.12). But we know that Antiochus argued that, by abandoning the full Stoic account of cognition and its commitment to cognitive impressions satisfying the complete Stoic definition, Philo succeeded only in bringing about the result he most wanted to avoid, namely that knowledge is impossible (Acad. 2.18). Presumably Antiochus drew on the case he had already brought against Academic probabilism to argue that impressions which fail to satisfy the full Stoic definition of the cognitive impression cannot provide a basis for judgment of any kind let alone judgments of the kind that deserve to be called knowledge.