In Paradoxa Stoicorum, the Roman philosopher Cicero defends six important Stoic theses. Since these theses seem counterintuitive, and it is not likely that the average person would agree with them, they were generally called "paradoxes". According to the third paradox, (P3), (all) transgressions (wrong actions) are equal and (all) right actions are equal. According to one interpretation of this principle, which I will call (P3'), it means that if it is forbidden that A and it is forbidden that B, then not-A is as good as not-B; and if it is permitted that A and it is permitted that B, then A is as good as B. In this paper, I show how it is possible to prove this thesis in dyadic deontic logic. I also try to defend (P3') against some philosophical counterarguments. Furthermore, I address the claim that (P3') is not a correct interpretation of Cicero's third paradox and the assertion that it does not matter whether (P3') is true or not. I argue that it does matter whether (P3') is true or not, but acknowledge that (P3') is perhaps a slightly different principle than Cicero's thesis. The upshot is that (P3') seems to be a plausible principle, and that at least one part of paradox III in Cicero's Paradoxa Stoicorum appears to be defensible.
Keywords: Cicero; Dyadic deontic logic; Stoic paradoxes; Stoicism.