This paper examines some neglected Chrysippean fragments on insecure apprehension (κατάληψις). First, I present Chrysippus’ account of how non-Sages can begin to fortify their insecure apprehension and upgrade it into knowledge (ἐπιστήμη). Next, I reconstruct Chrysippus’ explanation of how sophisms and counter-arguments lead one to abandon one’s insecure apprehension. One such counter-argument originates in the sceptical Academy and targets the Stoic claim that insecure apprehension can be acquired on the basis of custom (συνήθεια). I show how Chrysippus could defend the (...) possibility of custom-based apprehension, while also denying that there is custom-based knowledge. (shrink)