Diodorus Cronus (b. 4th Century BCE)

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(b. 4th century BCE)

Diodorus Cronus was born in Iasus, a port town in Caria (a region in the southwestern part of Asia Minor). He inherited his nickname 'Cronus' (old fogy) from his teacher Apollonius. All else that is known about his life must be inferred from anecdotal evidence, connecting him to Athens, where Zeno of Citium studied dialectic with him (cf. Diogenes Laertius 7.25), and to Alexandria, where he is acquainted with the physician Herophilus (cf. Sextus Empiricus, Pyrrh. Hypotyp. 2. 245) and where Callimachus mentions him in one of his Epigrams (cf. Diogenes Laertius 2.111) suggesting that Diodorus was known in the town. He may have died in Alexandria, some time after 290 BCE.

Since our sources attribute no writings to him, he probably left nothing written. Yet the reports on him show that he was an extremely influential figure in the generation that saw the founding of the Hellenistic schools of philosophy. He belonged to a philosophical sect known as the Dialecticians; these Dialecticianswere a school distinct from the Megarians. The name Dialecticians was not, as assumed in the older literature, another name for the Megarians (Sedley 1977). In physics, Diodorus was an atomist; he is said to have called atoms "partless" (Sextus Empiricus, Adv. Math. 9.363). One consequence of his atomism is that there are, according to him, no objects that move, only objects that have moved (Sextus Empiricus, Adv. Math. 9.363).

Diodorus's greatest impact was in the field of logic where, together with his pupil Philo the Dialectician, he seems to have laid the foundations of propositional logic. With Philo, he engaged in a controversy about the truthcriteria for the conditional; Philo favored a truth-functional analysis of the conditional, claiming that the conditional is true if and only if it is not the case that its antecedent is true and its consequent false (cf. Sextus Empiricus, Adv. Math. 8.113114), Diodorus gave a different account: According to him, a conditional is true if and only if it was not possible and is not possible that its antecedent is true and its consequent false (cf. Sextus Empiricus, Adv. Math. 8.115117).

Diodorus's repute as a logician, even to the present day, derives from his Master Argument, mentioned by several authors but reported explicitly only in Epictetus (cf. Epictetus, Diss. 2.19.15). Diodorus claimed that the following three propositions are incompatible: (1) Every past truth is necessary, (2) nothing impossible follows from what is possible, and (3) there is something possible that neither is nor will be true. Diodorus used (1) and (2) to argue for the falsity of (3), hence for a notion of possibility that defines the possible as that which is or will be true. Here again we find him contradicted by Philo, who defines the possible as that which, by the intrinsic nature of the proposition, is receptive of truth (cf. Boethius, De interpretatione ii, 234,10235, 9). The Master Argument became a bone of contention for Hellenistic logicians; it is still a matter of controversy how exactly Diodorus thought he could deduce the falsity of (3) from (1) and (2).

See also Atomism; Epictetus; Hellenistic Thought; Logic, History of; Megarians; Possibility; Zeno of Citium.



The testimonia on Diodorus are now conveniently brought together in Volume 1 of G. Giannantoni's Socratis et Socraticorum reliquiae (Naples: Bibliopolis, 1990, pp. 414435). Yet notice that in the account of the Master Argument in Epictetus, a line has been omitted from the text in Giannantoni's collection, so that only the first of the three propositions is quoted in full. The testimonia on Diodorus can also be found in K. Döring, Die Megariker (Amsterdam: Grüner, 1972).

works about diodorus cronus

Gaskin, R. The Sea Battle and the Master Argument. Berlin/New York: de Gruyter, 1995. Contains an extensive bibliography.

Prior, A. N. "Diodoran Modalities." Philosophical Quarterly 5 (1955): 205213.

Sedley, D. "Diodorus Cronus and Hellenistic Philosophy." Proc. Cambridge Philological Society N. S. 23 (1977): 74120. A pioneering study.

Vuillemin, J. Necessity or Contingency: The Master Argument. Stanford: CSLI Publications, 1996. Originally published in French as Nécessité ou contingence, 1984.

Weidemann, H. "Diodors Meisterargument und der Aristotelische Möglichkeitsbegriff." Archiv für Geschichte der Philosophie 69 (1987): 1853. Discusses extensively most of the literature up to the mid-1980s.

See also the four articles by H. Weidemann, R. Gaskin, M. J. White, and N. Denyer on the Master Argument in Logical Analysis and History of Philosophy 2 (1999) 189252. The articles are as follows: H. Weidemann, "'Aus etwas Möglichem folgt nichts Unmögliches'. Zum Verständnis der zweiten Prämisse von Diodors Meisterargument," 189202; R. Gaskin, "Tense Logic and the Master Argument," 203224; M. J. White, "The Lessons of Prior's Master Argument," 225238; and N. Denyer, "The Master Argument of Diodorus Cronus: A Near Miss," 239252.

Theodor Ebert (2005)

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