Not a page of the Logical Investigations survives, though it ran to many books; of Chrysippus's seven hundred and five works we have only fragments, quoted by other hands — often by his opponents.
Diogenes Laertius reports the saying that if the gods used dialectic, it would be none other than that of Chrysippus. It was he who fixed the five indemonstrable forms of argument — if the first, then the second; but the first; therefore the second — on which the Stoics built a logic of propositions, two thousand years before the moderns rediscovered it.
He wrestled all his life with the Liar and with the sorites, the paradox of the heap, advising the wise man to halt and fall silent before the fatal step. And the school itself said plainly: had there been no Chrysippus, there would be no Stoa.
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