Monday, October 27, 2014

Aristotelian propositions, promises and an open future

Aristotelian propositions are "tensed propositions" that are supposed to be able to change their truth value. If I say "It is sunny", this is supposed to express an Aristotelian proposition p such that p is true today, but p was false on cloudy days.

Now, a necessary condition for me to have fulfilled a promise is that

  1. the proposition that was the object of the promise is true.
Suppose yesterday—i.e., on Sunday—I promised:
  1. Tomorrow, I will do a blog post on Aristotelian propositions.
And I do make such a post today, i.e., on Monday, but I won't make another one on Tuesday. If the propositions expressed by tensed sentences are Aristotelian, then I have not fulfilled my promise. For the tensed proposition expressed by (2) is not true.

So tensed sentences don't express Aristotelian propositions, it seems. Rather, the proposition that yesterday I expressed with (2) is different from the proposition that would have been expressed with (2) today. The proposition that I expressed with (3) yesterday is "tenseless".

The advocate of Aristotelian propositions does have a way out. She can modify the condition (1) for promise fulfillment to:

  1. the proposition that was the object of the promise was true at the time of the promise.
Now, there is no difficulty. The Aristotelian proposition that would have been expressed by (2) was true yesterday (since today I do make such a blog post) but isn't true today (since tomorrow I won't—I hope!).

But note that the advocates of an open future cannot go for (3). For on their view, the proposition that was the object of the promise wasn't true when I made the promise. Thus, there is a tension between holding that tensed sentences express Aristotelian propositions and accepting an Open Future. But a lot of Open Futurists do just that.

This is not an insoluble difficulty. One can, for instance, suppose an operator By that acts on an Aristotelian proposition and "shifts it backward by y. Thus, B1 day applied to the Aristotelian proposition that tomorrow I will do a blog post on Aristotelian propositions is the Aristotelian proposition that today I do such a blog post. Then we replace condition (1) with:

  1. I fulfill at t2 a promise I made at t1 only if By(p) is true at t2, where y=t2t1 and p is the object of the promise I made at t1.
Still, it's weird, isn't it, that I fulfill a promise by bringing about something other than what I promised?

1 comment:

Michael Gonzalez said...

What if statements of what I "will do" are actually statements of what I "fully intend to do"? That could be true on the original day and not true now. You don't intend, today, to post about Aristotle tomorrow, but you did intend, yesterday, to post about it on the "tomorrow" of that day.

I don't think that a person saying "I will do X tomorrow" is trying to describe some tenselessly existing fact about tomorrow; he's stating an intention.