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Found the Master Argument in Epictetus, between two bus stops

Serkan Aydoğdu Fellow
· 4 replies
Possibility & necessityGreek & RomanStoicismArthur PriorChrysippusDiodorus CronusEpictetus#master-argument#possibility#stoic-logic
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Its coordinates: 1.6 Modality · 1.6.1 Possible Worlds

Another find from my recordings. Last week it was Epictetus, Discourses Book 2, and in the middle of a chapter he mentions an argument by Diodorus Cronus that clever people used to show off with. I had to pull my attention back to the road.

As far as I understand it, these three claims cannot all be true together:

  1. Everything true about the past is now necessary.
  2. Something impossible does not follow from something possible.
  3. Something is possible that is not true now and never will be.

Diodorus kept the first two and threw out the third. For him "possible" means "is true or will be true". Cleanthes gave up the first. Chrysippus gave up the second. And Epictetus, if I heard right, is not very interested in who won. His point is that a person can know all of this and still live badly.

Two things bother me. First, the recording said the actual argument, the steps that get from the three claims to a contradiction, has been lost. Is that true? Then how do we know it worked?

Second, if Diodorus is right, then if it is possible that I drive the 413 tomorrow, I will drive it. Something possible that never happens is not possible at all. That feels like the future is closed, even if it is closed by a definition. Is that what he meant, or am I reading too much into a word?

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4 replies

  1. Giulia Ferrante

    Fellow

    Yes, the derivation is lost. Epictetus is our main witness for the three claims and for who rejected which; Cicero's On Fate adds material on Diodorus and Chrysippus arguing about possibility. What we don't have is Diodorus's own proof, so every modern version is a reconstruction. That's partly why it's such a famous puzzle: everyone agrees it was impressive, nobody agrees on exactly how it went.

    And you are not reading too much in. Diodorus's definition makes "possible" mean "sometime true, now or later". Whether that closes the future or just redefines the word is precisely what the Stoics fought about.

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  2. Tomasz Szewczak

    Fellow

    One modern footnote. Arthur Prior's interest in Diodorus is part of how tense logic got started in the 1950s. He wanted to know what logic of possibility you get if "possible" just means "true now or at some future time", and the answer turns out to depend on the structure you give time: whether it's a line, whether it's discrete or dense, and so on. So Diodorus isn't only a museum piece. His definition became a test case.

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  3. Serkan Aydoğdu

    Fellow

    Thank you both. So if I take Chrysippus's side, I keep "possible" in the ordinary sense, and I accept that something impossible can follow from something possible. That sounds worse than Diodorus!

    Epictetus would tell me to stop worrying and drive the bus. I think I will, but I will keep listening.

    Helpful · 3
  4. Gerrit Venter

    Fellow

    Serkan, I coach under-16s, and on Friday I'll tell them that a win is possible on Saturday. If Diodorus is right I'm either lying or a prophet. I prefer Chrysippus for team talks. But your Epictetus is right too: the boys who can recite the tactics are not always the ones who play well.