 The outlines of Philo’s response to this problem in the Roman Books are fairly clear from the direct evidence we have for their epistemological innovations (Cicero Ac. 2.18 and Sextus PH 1.235). He argued, first, that the Stoic definition of the cognitive impression ruled out the possibility of anything being known—i.e., he restated the standard Academic arguments to this effect—and, secondly, that this definition was therefore misconceived, since at least some things could be known. His elucidation of the second claim is unfortunately not explicit in the surviving evidence. But its criticism by Antiochus (the context for Cicero’s report) very strongly suggests that Philo offered an alternative and weaker definition of knowledge of single propositions. For Antiochus both characterizes Philo’s innovations as an attempt to redefine “cognition” (Ac. 2.17 &amp; 2.18 fin.) and attempts to refute them by arguing that an impression that does not meet the condition given in the third clause of the Stoic definition (see  section 3.1  above) cannot be “cognitive”. Philo’s new definition thus amounted to something like the Stoic definition minus its third clause (the clause the Academics had always disputed). If so, Philo claimed that an impression is cognitive if it is both [a] true and [b] caused in the appropriate way for correctly representing its object—without adding the disputed Stoic rider [c], that its truth is warranted by the inimitable richness and detail of representation guaranteed by its causal history.