Philo the Dialectician (Greek:Φίλων;fl. 300 BC) was aGreek philosopher of theMegarian (Dialectical) school.[1] He is sometimes calledPhilo of Megara although the city of his birth is unknown. He is most famous for the debate he had with his teacherDiodorus Cronus concerning the idea of thepossible and the criteria of the truth ofconditional statements.
Little is known about the life of Philo. He was a disciple ofDiodorus Cronus, and was a friend ofZeno, the founder ofStoicism.Diogenes Laërtius states that Zeno "used to dispute very carefully with Philo the logician and study along with him—hence Zeno, who was the junior, had as great an admiration for Philo as his master Diodorus."[2]
Jerome refers to Philo as the teacher ofCarneades, which is chronologically impossible.[3] Diogenes Laërtius mentions a (presumably different) Philo who was a disciple ofPyrrho.[4]
One of Philo's works was calledMenexenus in which he mentioned the five daughters of Diodorus who were all distinguished dialecticians.[5] Two ofChrysippus' logical works were responses to books by Philo, one was directed at "Philo's Work on Meanings",[6] and the other at "Philo's Work on Moods".[7]
Philo disputed with Diodorus respecting the idea of thepossible and the criteria of the truth ofconditional statements.
In regards to things possible, Diodorus maintained that possible was identical with necessary, i.e. that possible is "that which either is or will be true".[8] Philo instead defined possible as "that which is capable of being true by the proposition's own nature",[8] thus a statement like "this piece of wood can burn" is possible, even if it spent its entire existence on the bottom of the ocean.[9]
Both Philo and Diodorus sought for criteria for the correct form of conditional propositions, and each of them did so in a manner corresponding to what he maintained respecting the idea of the possible. Philo regarded a conditional as true unless it has both a trueantecedent and a falseconsequent. Precisely, letT0 andT1 be true statements, and letF0 andF1 be false statements; then, according to Philo, each of the following conditionals is a true statement, because it is not the case that the consequent is false while the antecedent is true (it is not the case that a false statement is asserted to follow from a true statement):
The following conditional does not meet this requirement, and is therefore a false statement according to Philo:
Indeed,Sextus says "According to [Philo], there are three ways in which a conditional may be true, and one in which it may be false."[10] Philo's criterion of truth is what would now be called atruth-functional definition of "if ... then"; it is the definition used inmodern logic.
In contrast, Diodorus allowed the validity of conditionals only when the antecedent clause could never lead to an untrue conclusion.[10][11][12] A century later, theStoic philosopherChrysippus attacked the assumptions of both Philo and Diodorus.
This article incorporates text from a publication now in thepublic domain: Smith, William, ed. (1870). "Philon the Megarian or Dialectician".Dictionary of Greek and Roman Biography and Mythology. Vol. III. p. 312-313.
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