Further, arguments may be divided into true and false.
The former draw their conclusions by means of true premises; e.g. "If virtue does good, vice does harm; but virtue does good, therefore vice does harm."
Those are false which have error in the premises or are inconclusive; e.g. "If it is day, it is light; but it is day, therefore Dion is alive."
Arguments may also be divided into possible and impossible, necessary and not necessary.
Further, there are statements which are indemonstrable because they do not need demonstration; they are employed in the construction of every argument. As to the number of these, authorities differ; Chrysippus makes them five.
These are assumed alike in reasoning specifically conclusive and in syllogisms both categorical and hypothetical.
—Diogenes Laërtius, 7.79
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