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Core Concepts

Adequate Determinism
Alternative Possibilities
Causa Sui
Causal Closure
Chance Not Direct Cause
Chaos Theory
The Cogito Model
Comprehensive   Compatibilism
Conceptual Analysis
Could Do Otherwise
Default Responsibility
Determination Fallacy
Double Effect
Either Way
Emergent Determinism
Epistemic Freedom
Ethical Fallacy
Experimental Philosophy
Extreme Libertarianism
Event Has Many Causes
Frankfurt Cases
Free Choice
Freedom of Action
"Free Will"
Free Will Axiom
Free Will in Antiquity
Free Will Mechanisms
Free Will Requirements
Free Will Theorem
Future Contingency
Hard Incompatibilism
Idea of Freedom
Illusion of Determinism
Laplace's Demon
Liberty of Indifference
Libet Experiments
Master Argument
Modest Libertarianism
Moral Necessity
Moral Responsibility
Moral Sentiments
Paradigm Case
Random When?/Where?
Rational Fallacy
Same Circumstances
Science Advance Fallacy
Second Thoughts
Soft Causality
Special Relativity
Standard Argument
Temporal Sequence
Tertium Quid
Torn Decision
Two-Stage Models
Ultimate Responsibility
Up To Us
What If Dennett and Kane Did Otherwise?


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Free Will
Mental Causation
James Symposium

Master Argument of Diodorus Cronus

Diodorus Cronus was a member (or perhaps a late follower) of the Megarian School, whose arguments about the truth and falsity of statements about the future may have influenced Aristotle.

The so-called "Master Argument" (the κυριεύων or κύριος λόγος) was apparently first formulated by Diodorus, although we do not have his specific argument, because he wrote nothing (or at least nothing that survives). Like Socrates, he preferred talking (the dialectic) to writing. He was known as "The Dialectician."

Epictetus reconstructs the lost Master Argument as a logical contradiction between three propositions.

  1. every past truth must be necessary
  2. an impossibility does not follow from a possibility
  3. something is possible which neither is nor will be true
Given the first two, it is apparent that the third is false, and we can conclude that nothing is possible which is not true and never will be.

The Master Argument was central in the Hellenistic debates about determinism, as shown by Cicero's descriptions in On Fate.

For the ancients, and for modern sophists, this is the kind of logical linguistic argument used to prove that motion is impossible, Zeno's famous paradox. It is similar to Parmenides' dialectical proof that all the atoms must be in contact with one another, because there is a void (viz., nothing) between them.

Fundamentally, the Master Argument is a question abut the ontological status of the possible, the potential (δύναμις), as compared to the actual (ὁ κύριος). Epictetus' third proposition that something that neither is or ever will be is "possible" is just the common sense use of the term possible, phrased in such a way as to make it doubtful. How could something that neither is nor ever will be, be possible?

In his sophistic conclusion, that nothing is possible which is not true and never will be, Diodorus is playing language games with the meaning of "possible," just as modern compatibilist philosophers like Harry Frankfurt deny the existence of . Clearly, the Master Argument applies to the question of whether we are (or ever were) free to do otherwise.

Diodorus also argued that the actual is the only possible. He observed that if something in the future is not going to happen, it was therefore true in the past that it would not happen. From this correct observation, he mistakenly claimed that the existence of true statements about the future imply that the future is already determined.

This is the problem of future contingency, made famous in the example of Aristotle's Sea-Battle in De Interpretatione 9. Aristotle thought statements about the future lack any truth value. They are neither true nor false until the future time when they become true or false.

So a better way out might be to note that Diodorus' first proposition is dependent on the use of "truth," especially supposed "true" statements about the future, and we can reduce the Master Argument to the problem of future contingency.

The assumption that logical arguments and their "truths" are timeless is a misapplication of logic, which in any case cannot tell us much about the physical world.

Modern philosophers like C. W. Rietdijk, Hilary Putnam, J. J. C. Smart, Michael Lockwood, and Michael Levin like to think that the future is "already out there" in the relativistic space-time continuum of a "tenseless" "block universe."

Because special relativity can treat time as another dimension, philosophers mistakenly think it must have the properties of space, which is "already there." This is similar to the mistakes of both philosophers and mathematicians about chance. Since random events follow distribution laws, they must be lawful and therefore chance is not real, it is an illusion, like free will.

Modern determinists/compatibilists on free will like to argue that just as the past cannot be changed, so the future cannot be changed. "Change it from what to what?," says Daniel Dennett.

But note that the "truth value" of a statement made in the past can be changed when an event it describes does or does not happen, showing that some aspects of the "fixed past" (i.e., the truth values of past statements) "actually" have some changeability (when their potentials become actual).

Information Philosophy and Master Argument
Thinking about the Master Argument in terms of the growth of information provides the clearest resolution of the problem of future contingency.

Information is not a constant of nature. The cosmic creation process is constantly creating new information.

When information is created, there is always an irreducible chance element since it is quantum processes that form stable new information structures.

Some information about future events does not come into existence until the potential events become actual.

It is at that time that statements about the future acquire their truth values. Aristotle did not think in information terms, but he had the right answer to the Master Argument, one that disturbs modern logical positivists and analytic language philosophers, as shown by Richard Taylor's faux argument for Fatalism in the Psychological Review.

Note that Fatalism is a form of determinism. It is the simple idea that everything is already fated to happen, so that humans have no control over their future. But also note that Fate (personified) has arbitrary power and need not follow any causal or otherwise deterministic laws. It could include the miracles of omnipotent gods, in which case future contingency returns.

Note further that the gods' omnipotence contradicts the theological assumption that gods are omniscient. They cannot be both. That is a logical contradiction.

For Teachers
For Scholars
Epictetus on the Master Argument
Ὁ κυριεύων λόγος ἀπὸ τοιούτων τινῶν ἀφορμῶν ἠρωτῆσθαι φαίνεται: κοινῆς γὰρ οὔσης μάχης τοῖς τρισὶ τούτοις πρὸς ἄλληλα,
τῷ [τὸ] πᾶν παρεληλυθὸς ἀληθὲς ἀναγκαῖον εἶναι
καὶ τῷ [ἀ]δυνατῷ ἀδύνατον μὴ ἀκολουθεῖν
καὶ τῷ [*? δυνατὸν εἶναι ὃ οὔτ᾽ ἔστιν ἀληθὲς οὔτ᾽ ἔσται,
συνιδὼν τὴν μάχην ταύτην ὁ Διόδωρος τῇ τῶν πρώτων δυεῖν πιθανότητι συνεχρήσατο πρὸς παράστασιν
τοῦ μηδὲν εἶναι δυνατόν, ὃ οὔτ᾽ ἔστιν ἀληθὲς οὔτ᾽ ἔσται.
[2] λοιπὸν ὁ μέν τις ταῦτα τηρήσει τῶν δυεῖν, ὅτι ἔστι τέ τι δυνατόν, ὃ οὔτ᾽ ἔστιν ἀληθὲς οὔτ᾽ ἔσται, καὶ δυνατῷ ἀδύνατον οὐκ ἀκολουθεῖ: οὐ πᾶν δὲ παρεληλυθὸς ἀληθὲς ἀναγκαῖόν ἐστιν, καθάπερ οἱ περὶ Κλεάνθην φέρεσθαι δοκοῦσιν, οἷς ἐπὶ πολὺ συνηγόρησεν Ἀντίπατρος. [3] οἱ δὲ τἆλλα δύο, ὅτι δυνατόν τ᾽ ἐστίν, ὃ οὔτ᾽ ἔστιν ἀληθὲς οὔτ᾽ ἔσται, καὶ πᾶν παρεληλυθὸς ἀληθὲς ἀναγκαῖόν ἐστιν, δυνατῷ δ᾽ ἀδύνατον ἀκολουθεῖ. [4] τὰ τρία δ᾽ ἐκεῖνα τηρῆσαι ἀμήχανον διὰ τὸ κοινὴν εἶναι αὐτῶν μάχην.

The argument called the ruling argument (ὁ κυριεύων λόγος) appears to have been proposed from such principles as these: there is in fact a common contradiction between one another in these three propositions, each two being in contradiction to the third. The propositions are,

that every thing past must of necessity be true;
that an impossibility does not follow a possibility;
and that a thing is possible which neither is nor will be true.
Diodorus observing this contradiction employed the probative force of the first two for the demonstration of this proposition,
That nothing is possible which is not true and never will be.
Now another will hold these two: That something is possible. which is neither true nor ever will be: and That an impossibility does not follow a possibility. But he will not allow that every thing which is past is necessarily true, as the followers of Cleanthes seem to think, and Antipater copiously defended them. But others maintain the other two propositions, That a thing is possible which is neither true nor will be true: and That everything which is past is necessarily true; but then they will maintain that an impossibility can follow a possibility. But it is impossible to maintain these three propositions, because of their common contradiction.
Epictetus continues:
If then any man should ask me, which of these propositions do you maintain? I will answer him, that I do not know; but I have received this story, that Diodorus maintained one opinion, the followers of Panthoides, I think, and Cleanthes maintained another opinion, and those of Chrysippus a third. What then is your opinion? I was not made for this purpose, to examine the appearances that occur to me, and to compare what others say and to form an opinion of my own on the thing. Therefore I differ not at all from the grammarian.

Chapter 3.7 - The Ergod Chapter 4.2 - The History of Free Will
Part Three - Value Part Five - Problems
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