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So, in modal logic class yesterday we were going over a claim Aristotle made (2500 years old and still relevent, too bad he couldn't count women's teeth), where he says that future-tense sentences aren't true or false. Now, lots of people have had a go at giving their own explanation of why this is right or wrong, but we spent most of our time on one of the premises of his argument, which is a pretty interesting argument in itself. Aristotle says that what is true is necessarily true, a claim he cashes out as follows:
if a thing is white now, it was true before to say that it would be white, so that of
anything that has taken place it was always true to say that a thing is or will be,
it is not possible that it should not be or not be about to be, and when a thing
cannot not come to be, it is impossible that it should not come to be, and when
it is impossible that it should not come to be, it must come to be. All, then, that
is about to be must of necessity take place.
So, breaking it down, it becomes something like this:
For some event 'e':
(i) If ‘e is happening’ is true, then ‘e will happen’ was always true.
(ii) If ‘e will happen’ was always true, e cannot not happen.
(iii) If e cannot not happen, then it is necessary for e to happen.
Conclusion: If ‘e will happen’ was always true, it was necessary that e e would happen.
I think this is a very smart thing to say. It takes a fact about how we use words, comes to an informative conclusion, and each step of the way teaches us something about how we actually use modal terms in our vocabulary, terms like 'possible', 'necessary', etc. Since modal logic is the project of trying to make clear how truth and falsity works, this argument seems to be modal logic from the top shelf.
Let's look at the premises in order:
(i) is the one which does all the work, I think. It captures something non-obvious about the way we track the truth of statements made at some time throughout the timeline, ie, if I say tonight that 'Auckland will wring the rugby tomorrow', meaning that on Sat 26 April 2008 Auckland will win the rugby, and it turns out that they do, I would have been right now to say what I did. If I said it yesterday it would have been true as well, in fact, if I had made that claim at any time throughout history, it would be true (let's not be confused by the indexical 'tomorrow', I'm not saying that, whatever day we might consider, Auckland will win the rugby the day after, but pointing to tomorrow, 26 April 2008). For instance: people often wail on Marx for predicting that it is inevitable that the workers of the world would bring about communism through revolution, because in the absence of such a revolution it seems like his claim turned out to be false, but if this revolution were indeed to happen, then Marx would have been right all along. So, if some event occurs, saying that that event would occur would always have been true.
(ii) might be a tautology, but attached to (i) it becomes an informative claim. The tautology is: if something were always true, then it could never have been false. (ii) is: if it were always true that some event would happen, then that event never could not happen.
(iii) brings about the conclusion, and is another tautology: if something cannot not happen, it was necessary for it to happen. This seems to be what 'necessary' means. And attached to (i) and (ii) we have come to the conclusion: if something happened, it was necessary for it happen. We started off with an observation of what we typically think is true, added the meanings of words at work, and have ended up supporting a substantive claim. Great stuff.
So, is everything that has happened actually inevitable? The above argument certainly gives you reasons to think that it is. There are points where you can put pressure on it, of course: the most important point would be whether we should accept that the way we use modal terms in our vocabulary actually accurately represents possibility and necessity in the world as it is. If you are going to reject the conclusion about the inevitability of events, then you're going to have to say that we simply have possibility and necessity wrong, and our use of modal terms need to be revised. That, or poke a hole in the argument.
[The following is probably only of interest to those who care about modal logic. You've been warned. I searched for good sources to look at if you quickly want to know what 'model K tau-rho' and things like that means, but trust me, those I found were all pretty technical and you're better off not reading any of them. If you start losing interest in what follows, jump to after the next set of square brackets for more open-to-anyone chin-scratching.]
People normally try the latter route, and they have had 2500 years to go about it. Recently, after some formal logical systrems for modal logic have been developed (only since the 1950s, since formal logic is a very recent field), some have shown that, in the best of these models, either (ii) or (iii) isn't a tautology, and thus, that the argument doesn't follow. This is true in the modal logic system most people consider the best candidate for actually reflecting the way we use modal terms, model K tau-rho, also called S4 (all of that means something, but formal logic is as opaque to non-logicians as any formal field is to outsiders). Accordingly, Aristotle is often said to have been guilty of a 'modal fallacy'. I could do the formal logic work on this point if anybody is interested (I don't think anybody would be - those folk who are really into this stuff already know it, and most people simply aren't that interested), since it would just be me doing my homework. A point worth making: there are dozens, if not hundreds, of different modal logics in circulation, each of which with slightly different rules and preconditions, etc, eachl of them trying to show some feature of our modal vocabulary, all of which is in service of determining what modal logic is the correct one for making sense of what we mean with truth and falsity. Model K tau-rho is merely the current favourite for being the 'correct' modal logic.
The long and short of all this is that my reply is: so much for model K tau-rho. It is the job of modal logics to give an explanation of how these modal terms work. It's an open question whether model K tau-rho actually accomplished this, while Aristotle's arguments make no use of any formal system but only rely on the meanings of words in our natural language - significantly, meanings that persist in the modal vocabulary of any language, as far as I know. So, Aristotle has clearly latched onto how modal terms work in our natural language, and if model K tau-rho, or any other formal model, disagrees, then it is probably the one that is wrong, not Aristotle. Since Aristotle is not making a point about modal logics in general, but about the modal logic we actually use, his non-adherence to formal systems developed 2500 years after the fact is simply irrelevent. (If I had done all the formal logic work here, I could have showed how, while it tells a plausible story of how we use 'possible' and 'necessary', model K tau-rho doesn't have anything like what is implied by premise (i), a way of tracking the truth of some proposition from time to time, and that that is probably where model K tau-rho goes wrong).
[Here ends the more opaque modal logic stuff]
So, what now? One way we can square the conclusion of 'what has happened was necessary to happen' with how we that multiple realities are possible is as follows: while it might seem that there are a lot of possible futures which could be played out, it is a matter of fact that we have only one actual past. While it might seem to me now that there are a lot of ways tomorrow will work out, by this time tomorrow I would also have only one actual past. I can continue this worm forwards, until it is clear that there is in actuality only one time line, and that other possibilities have turned out to be phantoms born out of my ignorance of how the world actually will turn out. Perhaps you want to resist this, because this is too strong a conclusion to be drawn out of something as simple as saying 'the weatherman was right that it wouldn't rain today'. I'd disagree with you, listing the reaosns I've given above, but we'd be busy with an interesting discussion.
In the spiel above there's a lot of places someone might go 'no, now wait a moment, that's not right' and argue against what I've been arguing. Anyone interested?
Anyway, like I said, I was very impressed by this little argument. It's all smart and stuff. |
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