According to Presentism, whatever exists, exists now, in the present. The past has flowed away and the future is yet to come. Only the present exits. But what of things like abstract objects? This view appears to rule out in one swift stroke, any view of abstract entities, for such things do not exists at times, present, past, or future. Many presentists would want qualify a bit. According to this qualified view, for any x, x exists if and only if x obtains in the present, and x is non-abstract. This way room is made for the existence of atemporal objects—objects like properties or numbers which exist but do not exist in the present since they do not exist at any time.
But as attractive Presentism is, it faces a serious objection: How exactly are truths about the past grounded? This question of the grounding past truths is a consequence of the truthmaker thesis:
TM: Every truth has a truthmaker—that in virtue of which a proposition or sentence is true.
Traditionally, facts or states of affairs are taken to be the sort of things that qualify as truthmakers, so that for any true proposition P, there exists a corresponding fact or state of affairs S such that P if and only if S. But perhaps this definition is too strong. There are some truths, e.g. analytic ones, which seem to require no truthmakers. For example the proposition
1) All bachelors in are unmarried,
is just true by definition. Similarly, contingent negative existential propositions like
2) Cerberus does not exist,
are also thought to not require truthmakers since they do not posit the existence of anything and, so, do not require the existence of anything in order to be true. But save for the likes of 1) or 2), truthmakers are apparently needed for all other propositions. If it is true that I am now writing this post, then necessarily, it is the case that I am now writing this post. But what about the post I wrote last Saturday? What is it that grounds a proposition like:
3) Xavier wrote a post last Saturday.
Given Presentism, apparently, nothing in the past could, since past events do not exist. Further, nothing in the present does either, for my typing last Saturday’s post occurred last Saturday. How then does Presentism account for the truth of something like 3)?