The above title gives the gist of presentism in the philosophy of time. It is an answer to Quine's ontological inventory question: What is there? What, by category, should we count as existent? The presentist answer is that only (temporally) present items exist: wholly past and wholly future items do not exist. Among these items are times, events, processes, individual substances, property-instantiations.
'Only the present exists' is doubly ambiguous.
FIRST AMBIGUITY
It is first of all ambiguous as between a tautology and a substantive thesis. It depends on how one construes 'exists.' Is it present-tensed? Then we get a tautology:
TAUT: Only the present exists at present.
Presentists, however, are not in the business of retailing tautologies. They are out to advance a substantive and therefore non-tautological claim about what exists. But to do this, their characteristic thesis cannot sport a present-tensed use of 'exists.' So they have to say something like this:
SUBS: Only the present exists simpliciter.
But what does 'simpliciter' mean? One might take it to mean 'tenseless.' Thus
SUBS*: Only the present exists tenselessly.
That is not a tautology. One might reasonably object that (SUBS*) is false on the ground that there are (tenselessly) wholly past and wholly future items such as Julius Caesar, his assassination, and my death. That is what the so-called 'eternalists' maintain:
E: Past, present, and future items all exist tenselessly.
All existents are on a par in point of existence. All are equally real. Boethius exists just as robustly (or as anemically) as I do. It is just that he exists in the past. Now most eternalists are B-theorists. They accept the B-theory of time. And so they would say that 'past,' 'present,' and 'future' can and must be cashed out relationally in terms of the B-relations: earlier than, later than, and simultaneous with. Boethius exists in the past in that he tenselessly exists at times earlier than some reference time such as the time of my writing this sentence. He exists just as I do, but elsewhen. London is elsewhere relative to here, where I flourish, but is no less real than where I flourish. Gloomier, no doubt, but no less real.
The main thing for 'present' purposes is that presentism and eternalism are both substantive claims. Neither is a tautology and neither is a contradiction. Note also that if 'exists' in 'Past, present, and future items all exist' is read present-tensedly, then the sentence just mentioned would be a contradiction. We also note that to formulate either presentism or eternalism we must invoke a tenseless sense of 'exists.'
SECOND AMBIGUITY
Now we notice that 'Only the present exists' is also ambiguous as between
SPM: Only this present exists: there is (tenselessly) exactly one time, the present, at which everything (tenselessly) exists.
and
PP: Only the present present exists: there are (tenselessly) many times, and every time t is such that everything that exists exists (tenselessly) at t.
The first view is Solipsism of the Present Moment. This is a lunatic view, although it seems logically possible. It amounts to saying that everything that ever existed and everything that ever will exist exists now. Imagine that the entire universe, together with fossils, monuments, memories, and dusty books just now sprang into existence, lasts a while, and then collapses into non-being.
Presentism as usually understood affirms something like (PP), which implies that there are past presents, a present present, and future presents. The idea is that, at any given time, whether past, present, or future, all that exists is what exists at that time. If reality is the totality of what exists, (PP) implies that reality is always changing. (PP) implies that reality is 'dynamic' whereas (E) implies that it is static.
(PP) strikes me as problematic. (PP) implies that there are (tenselessly) many different times. But there cannot be (tenselessly) many times if at each time there is only what exists at that time. For if at each time there is only what exists at that time, then at each time there are no times other than that time. Is there a formulation of presentism that is consistent with its own truth? I suspect that there isn't.
Presentism is at present very popular among philosophers. I am wondering why. Some distinguished writers actually say that it is common sense. What? The proverbial man on the street has no opinion on any of these questions.
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