Master Argument

The professor smiles and offers you a meandering lecture on the matter...

Ah yes, Diodorus was actually famous for more than just the Master Argument, you know. He came up with arguments like the "Veiled One" and the "Horned One". His works were so often rehearsed and debated that even the birds learnt them by heart, and they would sing them from the rooftops. People would even chalk on the walls, "Diodorus Cronos is wise", hah.

But that was not your question; let me try to focus. You want to know about the Master Argument, which in antiquity was also known by the title On the Possible. It is comprised of three assertions, but only two of them can be true. For taken together, the three will result in a contradiction. Let me list them for you:

  1. One, that every past truth is necessary.
  2. Two, that an impossibility does not follow a possibility.
  3. Three, that a thing is possible which neither is nor will be true.

Diodorus recognised the truth of the first two, and therefore rejected the third. He makes these choices because he wishes to ensure that potential complies with the Eleatic understanding of ontological necessity. If something can happen, it necessarily does so at some point. The idea of absolutely undetermined possibilities, the idea that things can switch from true to false, it's all nonsense. I'll go through line by line, and I hope you'll see the beauty of the puzzle our friend has presented to us.

I take point one to signify that past events and facts are set in stone. For example, you walked into this room, that event cannot be denied or changed. For point two, I understand the possibility to be a future event that will occur in the chronology. The impossibility will be an event that will not occur in the chronology. The impossibility could be a fanciful idea we are considering, perhaps in the next sixty seconds I will jump into the sky and leave orbit. That event won't occur in the chronology, so it's impossible.

The third assertion should be immediately suspect to anyone who has thought at length about metaphysics. At any rate, in the context of the Master Argument, it does not stand in harmony with the other two because it relies on an indeterminate and non-branching chronology. For purposes of point three, let us say it is possible that in five minutes, the ground will open and swallow us whole. Prior to the event's time frame completing, it is indeterminate and therefore not yet true, and when the time frame completes we can say it is false.

Now let us skip forward an hour and review. Per point one, everything in the past is necessarily true. So, it is true that in the past there is this possibility of the ground swallowing us whole in a particular five minute span. Further, it didn't happen, so it's true that that this possibility is an impossibility. Yet, what we have now identified as an impossibility is following from a possibility, that is to say it's an impossible event that is immediately following the possible event of you entering this room.

If we wish to maintain point three, we must either break with point one, the idea that everything persists in the past and/or is set in stone there, or point two, that an impossible event doesn't follow a possible one. In fact, we know that there are some famous people in antiquity that did maintain a different combination of the points. Yet as I hinted earlier, there are insurmountable metaphysical objections to point three.

Sadly we do not receive the Master Argument directly from Diodorus, his works are largely lost. We have some detailed testimonia and some very brief quotes, and this rendering of the Master Argument is actually from a much later Stoic author.

Anyway, these matters will all be explored in detail another time, when these exhibits are complete. Which I should return to, so please forgive me if I stop things here. I would highly recommend you check out the general exhibits on Change, or perhaps retire to our guesthouse. Perhaps I'll have everything up and ready tomorrow!

The man smiles broadly at the idea of having his exhibits ready for public viewing. You decide to...


  1. Thank the professor for his time and move on to the general exhibits...
  2. Wish the professor goodbye then head off to the guesthouse...