  Arguments are—normally—compounds of assertibles. They are defined as a system of at least two premises and a conclusion (D. L. 7.45). Syntactically, every premise but the first is introduced by ‘now’ or ‘but’, and the conclusion by ‘therefore’. An argument is valid if the (Chrysippean) conditional formed with the conjunction of its premises as antecedent and its conclusion as consequent is correct (S. E. PH 2.137; D. L. 7.77). An argument is ‘sound’ (literally: ‘true’), when in addition to being valid it has true premises. The Stoics defined so-called argument modes as a sort of schema of an argument (D. L. 7.76). The mode of an argument differs from the argument itself by having ordinal numbers taking the place of assertibles. The mode of the argument