Sunday, February 05, 2006

In Defense of Prior's 'Peircean' Tense Logic

I just finished a paper defending what philosopher Arthur Prior called the "Peircean" system of tense logic over against the rival "Ockhamist" system.

You can download the paper here (100kB, PDF).

I'll be reading this paper at the group meeting of the Philosophy of Time Society at the Pacific APA conference in March.

For some more background on the Peircean / Ockhamist tense-logic debate, follow this link to an earlier blog post on the topic.


At 2/10/2006 12:45 AM, Blogger Ocham said...

Hello Alan. Quite an involved argument here, and I'm not sure how the bits are connected. You characterise presentism as

Presentism = the view that all of reality exists now, in the present

How does this connect with your argument that proposition about the future is a now true then it is true in virtue of what is now the case? Suppose an Ockhamist agrees that it is NOW the case that it will rain. Does that commit him to the view that not all of reality exists now? What part of reality is implied to exist, that doesn't yet exist?

Also, I don't see how the argument about causal force connects the one here.

At 2/10/2006 12:46 PM, Blogger Alan Rhoda said...

Hi Ocham,

Given presentism, there are no non-present states of affairs. Given the correspondence theory of truth, a proposition is true iff the state of affairs it posits obtains. Hence, given presentism + correspondence, a proposition can be true iff what it posits obtains now, in the present. Hence, if anything is true about the future, then it is true in virtue of some presently obtaining state of affairs.

As for 'Ockhamism' (as Prior defines it), commitment to IS(p) implies WAS(WILL(p)) means that past truths are retroactively grounded by future facts. Hence, the Ockhamist would say that it is now the case that it will rain tomorrow because when tomorrow comes it does rain. Now, I think an Ockhamist who is a B-theorist can get away with this, but I doubt that an A-theoretical Ockhamist can, especially if he also believes in future contingents. Because on an A-theory the future is either non-existent or metaphysically unstable, it cannot serve as a stable ground for present truths about the future. So I think the A-theoretical Ockhamist believer in future contingents is either going to have to reject correspondence, reject the A-theory, or, more radically perhaps, follow Storrs McCall and say that all causally possible futures really exist, deny bivalence, and allow that past truths about the future can change.

The semantic argument based on causal force is intended to show that the Peircean definition of the future tense operator WILL() as carrying determinative causal force is more natural and better accommodates the assertibility of propositions about the future. The metaphysical argument based on grounding reinforces this conclusion by arguing that, on an A-theory of time, truths about the future are more plausibly thought of as grounded in present causal tendencies, as the Peircean would have it, than in the future, as the Ockhamist claims.

At 2/11/2006 7:31 AM, Blogger Ocham said...

If you bring 'states of affairs' into it, your argument is valid. For every true statement there must be a state of affairs - some structure or set of things, hence some existing structure or set of things, which, because it exists (present tense) exists now.

But that begs the question. Why should we believe in the existence of 'states of affairs'. That is exactly the sort of thing that on Ockhamist is likely to deny!

At 2/15/2006 3:38 PM, Blogger Alan Rhoda said...

Hi Ocham,

Couple points. First, I'm specifically arguing against Prior's "Ockhamist", the person who thinks that IS implies WAS(WILL). Other aspects of Ockham's philosophy, such as his nominalism, are peripheral to my argument. One can be a tense-logical "Ockhamist" without being a full-fledged Ockhamist.

Second, I don't think I'm presupposing anything regarding "states of affairs" that is, or ought to be, controversial--at least not for anyone who endorses a correspondence theory of truth. In fact, all I need is an intelligible distinction between what is thought to be the case on some occasion and what is the case, a distinction that should be clear to anyone who's ever made a mistake and later realized it. By "state of affairs" I mean merely something that can be thought to be the case. By the "obtaining" of a state of affairs, I mean merely it's being the case. If Ockham wants to take issue with that, then I say so much the worse for Ockham. Can anyone seriously maintain without self-contradiction that there is nothing that can be thought to be the case?



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