Cicero’s mistake and denied conjunctions: did stoic logic include six indemonstrables?

Cicero attributes an inference schema that is not logically valid to Stoic logic. This fact has been deemed as a Cicero’s mistake. However, in this paper, I assume the thesis that Cicero was not actually wrong and that, by means of his schema, he could be showing us interesting aspects of Stoicism that are not clear in the ancient sources. In this way, I use the mental models theory as a methodological tool and argue that the case of Cicero’s mistake allows us to suppose that there were six indemonstrables in Stoic logic, and not five.