Philo of Megara (c. 400s BCE)

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PHILO OF MEGARA
(c. 400s BCE)

Very little is known about the life of Philo of Megara, or Philo Dialecticus. Since he was a pupil of Diodorus Cronus at the same time as Zeno of Citium, the founder of the Stoa (cf. Diogenes Laertius, DL 7.16), he was very probably active in Athens in the last decade of the 4th century BCE. He was not, as is assumed in the older literature, a member of the Megarian school of philosophy, but belonged to a separate sect, the Dialecticians. Hence there is no reason to make Megara his birthplace. From the titles of two lost treatises by the Stoic Chrysippus that were directed against Philo, we learn that Philo wrote On Signs (DL 7.191) and On Moods (of Argument) (DL 7.194). He also wrote a dialogue called the Menexenus, in which the five daughters of the Dialectician Diodorus Cronus, all of them also Dialecticians, were made to appear. It is possible that the theory of signs referred to in Pseudo-Galen's Historia philosopha c. 9 as belonging to the "dialecticians" goes back to Philo's treatise. The logical terminology in this report is in accordance with that used by the Dialecticians, and the epistemological terminology does not yet show Stoic influence. Signs are here defined as a special class of conditionals, namely sound conditionals with a true antecedent revealing the consequent. We are on safer ground with two other claims attributed to Philo, one concerning implication, the other the definition of modal concepts.

Philo argued that a conditional is true if and only if it is not the case that its antecedent is true and its consequent false (cf. Sextus Empiricus, SE Adv. Math. 8.113–114). Hence Philo seems to have given for the first time a truth-functional definition of the conditional. Against this claim, Diodorus Cronus held that 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. SE, Adv. Math. 8.115–117). Thus the conditional "If it is day, I am talking," which proves to be true, according to Philo, provided that I am talking while it is day, will be false according to Diodorus. Although Sextus Empiricus in his report on this dispute has the consequent "follow" from the antecedent, it is not clear whether Philo and/or Diodorus want to make their criteria for the truth of the conditional a sufficient condition for the validity of an argument. It would have rather bizarre consequences in both cases: For Philo, any true propositions would entail each other, and for Diodorus, any true propositions about the past would entail each other.

Philo defines the possible as that "which, by the intrinsic nature of the proposition, is receptive of truth"; he defines the necessary as that "which, since it is true, by its own nature, is never receptive of falsehood". Similarly, the non-necessary is defined as that "which by its own nature is receptive of falsehood" and the impossible as that "which according to its own nature could never receive truth" (cf. Boethius, De interpretatione ii, 234). Here again he disagrees with Diodorus, who defines the possible as that "which either is or will be (true)." For Diodorus there can thus be no unrealized possibilities, whereas this is possible with Philo. Philo's modal logic, like that of Aristotle, seems to be based on an essentialist epistemology.

See also Chrysippus; Diodorus Cronus; Zeno of Citum.

Bibliography

works by philo of megara

The testimonia on Philo are to be found together with the material on Diodorus Cronus in vol. 1 of G. Giannantoni, Socratis et Socraticorum reliquiae. Naples: Bibliopolis, 1990, pp. 414–435. For a possibly Philonian theory of signs see: H. Diels. Doxographi Graeci. Berlin: Reimer, 1879, p. 605 (Pseudo-Galen, Historia philosopha c. 9).