Other writings     Drawings gallery

Presentism, Penguins & The Le Poidevin-Russell Prong

Can the presentist escape the Last Thursdayism objection against truthmaking?

ThursdayI shall argue the Last Thursdayism objection against presentist truthmaking is inescapable; since it is a consequence of a sole existing privileged present – intrinsic to all presentisms – and not of any particular presentist truthmaker theory. I shall consider how the truthmaker theories of Rhoda and Cameron fare against the objection – the former because of its unique relevance to the objection; the latter because it is the most sophisticated presentist truthmaker theory.

Presentism is the position that only the present exists. An easy way to understand this is that time-travel – of the meet-your-past-or-future-self variety – would be impossible since there would be no past or future to travel to (this might be simplified but this essay is not about presentist time-travel logistics and I’m only using them as a spring-board).

A worry for presentism is therefore that there are not enough existing things to enable saying anything true or false about non-present events. Usually we do not mind this regarding the future but we want there to be a fact of the matter about how much money our lazy friend loaned off us yesterday. However, if yester-friend no longer exists; if we cannot enter our TARDIS, go back, and observe ourselves handing over those hard-earned 20 pounds, then what makes our friend wrong to say he most certainly never received any monetary assistance, thank you very much? We should, want to say that there are facts about the present situation incompatible with his claim – he now owns 20 toy penguins from the pound store, say, which he would not have owned without our Samaritanism. However, who is to say he could not have come into possession of said penguins by other means?

Le Poidevin sums up this conundrum nicely in his book Travels in Four Dimensions:

[If] any number of pasts are compatible with the present state of affairs, and it is only the present state of affairs that can make true or false statements about the past, then no statement about the past is either true or false. What is now the case, as we might put it, underdetermines what was the case. So, to guarantee a definite truth-value to every statement we might make about the past (i.e. to guarantee that every such statement will be determinately true or determinately false), the presentist has to assume that only one past is compatible with the present state of the world: only one course of history could possibly have led up to this point (pp. 138-39).

The presentist faces the daunting task of collapsing all imaginable pasts into a single possible history using naught but her wits and present ontology. The core-thought is that facts need to be anchored to solid existence. There are various ways to explicate this truthmaking principle ranging from the nearly non-commital “truth supervenes on existence” to the immensely demanding “For all worlds w and v, and all propositions p, if p is true at w but not at v then there is (possibilist quantifier) some thing that exists at w and not at v, or vice-versa (Cameron).”

It is not within the scope of this essay to argue neither for the most plausible version of truthmaking nor for the correctness of the theory in general. Although it might be an option for the presentist to reject truthmaking altogether, I shall assume its veracity. Ideally a presentist apologist should want to tackle the strongest version of truthmaking (as does Cameron) and a presentist critic should want to derive a conflict from the weakest. Since I argue that the worry of Last Thursdayism arises from the privileged present and not any particular truthmaking theory, I invite picking whichever truthmaker is most comfortable.

Flying Spaghetti Monster[The Flying Spaghetti Monster] then spent the next ten to one hundred years painstakingly preparing the universe to appear older than it actually is (Henderson, p. 67).

Last Thursdayism is an internet mock-religion claiming the entire world was created last Thursday complete with a deceptive appearance of an older history. There are other similar hypothetical scenarios but ‘Last Thursdayism’ is especially evocative. I use the term in reference to any proposition about the coming into being of a deceptively young world at any arbitrary time (and by any means). Bertrand Russell was, despite a different context, particularly lucid:

Bertrand RussellThere is no logical impossibility in the hypothesis that the world sprang into being five minutes ago, exactly as it then was, with a population that “remembered” a wholly unreal past. There is no logically necessary connection between events at different times; therefore nothing that is happening now or will happen in the future can disprove the hypothesis that the world began five minutes ago. Hence the occurrences which are called knowledge of the past are logically independent of the past; they are wholly analysable into present contents, which might, theoretically, be just what they are even if no past had existed (Russell, 1921, p. 159).

If we now couple Le Poidevin’s thoughts with Russell’s  the problem of Last Thursdayism for presentist truthmaking becomes immediately clear. If it is both true that “the presentist has to assume […] only one course of history could possibly have led up to this point” and that there “is no logical impossibility in the hypothesis that the world sprang into being five minutes ago,” then the presentist has already lost!

Now, obviously the presentist should say we were being too hasty. Firstly, the presentist might, as earlier mentioned, cast away truthmaking entirely. Maybe past truths are just primitive with no additional requirements. I take this as a matter of personal disposition and assume – just as brutely – that this is false. Secondly, the presentist could hold that Le Poidevin’s truthmaking is unreasonably strong or insist that what it truly means to state a truth about the past is counter-intuitively not to say something about what actually happened, since that is now lost to unreality anyway, but to say something about backwards extrapolation from our current state of affairs – i.e. relegate ‘past truths’ from the logical and metaphysical to the nomological. I shall return to this shortly.

Thirdly, the presentist could reject Russell. There is some merit to this but it is beyond me to argue for it. Perhaps a capable presentist could argue for the logical impossibility of creatio ex nihilo, the impossibility of a ‘batteries included,’ ‘straight out of the box’-ready world, and the impossibility of a mischievous creator. Interestingly enough this brings us to ‘fourthly.’ Alan R. Rhoda argues that God’s memories could serve as presentist truthmakers for the past. I must admit I am not impressed with the solution but since the Last Thursdayism objection is undeniably close to the possibility of mischievous theism (though it can work without) it would be benighted of me to neglect the argument that the very same deity’s memories could ground the truth of said subterfuge.

The reason for my reservations is that Rhoda’s solution is too dependent on one’s prior religious views. If God is already included in your ontology, great! Please apply its explanatory capacity to presentism (though what if God sprang into existence last Thursday complete with false memories?) Now, far be it from me to guess about a fellow philosopher’s religiosity but inasmuch as Cameron is not already a theist for non-presentist reasons, he should find the God solution unsatisfactory for the same reason he considers ‘The Actualiser’ solution unsatisfactory:

Ross P. CameronIf I’m allowed to postulate whatever I like, with whatever essential properties I like, then of course for any true proposition I can always postulate some thing or things that couldn’t exist and that proposition be false. At its simplest, I can always postulate the fact that p for any true proposition p. Or I can postulate the existence of The Actualiser: an entity whose essence is so tied to actual truth that it would not exist were any proposition that is actually true false.

Cameron goes on to explain constraints on truthmaker positing, namely 1. Presentism, that “every thing that exists unrestrictedly exists presently,” 2. Realism about the past, that “there are true propositions concerning how things were, and the truth of such propositions is independent of our beliefs about how things were and our evidence as to how things were,” and 3. Present intrinsic nature, that whatever property of an object we posit to explain how something was, the property should also tell us something about how the object is in and of itself right now (paraphrasing).

Ancient Of Days - William BlakeTo be fair to Rhoda, he champions God because “it is not vulnerable to the charge of metaphysical ‘cheating’ […]” since “there are many independent reasons for thinking that God exists.” Be that as it may, if we do not already accept any such reason, the God solution is cleverly disguised anti-realism, since there is no reason why ‘our beliefs’ should exclude God’s beliefs – does God remember the past because it is true, or is it true because God remembers it (borrowing from Plato, Grube, p. 12)? This returns us to ‘secondly.’ Relegating past truths to the nomological also constitutes anti-realism about the past, since it amounts to the truth of propositions concerning how things were being entirely dependent on our current evidence.

Cameron fares much better at attempting circumvention of the Le Poidevin-Russell prong and the careening into either anti-realism or the steep demand of collapsing all imaginable pasts into a sole possibility. To Cameron the truthmaker of past truths about an object is its distributional property – i.e. a property that says how the object is across a period of time. This enables Cameron’s ontology to accommodate objects with intrinsic natures at a time (the present) that are multiply realisable by contradistinct distributional properties. Quite a mouthful, but it means Cameron is free to claim that even though more than only one course of history could possibly have lead up to this point, it does not render ‘this point’ underdetermined with no true or false statements about which course of history is true, since ‘this point’ presently has a distributional property determining it.

Admittedly, this is clever truthmaking but while Cameron is clearly off the hook from having to collapse all present-compatible pasts, I shall still insist he has to collapse one. Cameron collapsed the pasts without really doing so. While we now can allow multiple possible pasts leading to an object’s present intrinsic nature, there must still be only one possible past leading to an object’s present distributional property. Cameron simply changed the compatibility condition. So in order to reintroduce the problem all we need is an additional possible past leading to the same distributional property.

Given a privileged present and present-exclusive ontology – with distributional properties existing solely in the now – Last Thursdayism is precisely such a possible past. Suppose God created the world five minutes ago. Could She not imbue an object with any presently existing property – even distributional? This is easier to consider in eternalism in which all times exist equally. God can at time t5 create times t1 to t10, in which case an object at t5 springs instantly into existence complete with its t1-t10 distributional property. This poses no problem for the eternalist, since she has no privileged present; for the eternalist there are truths about t1 at t5 regardless of reckless temporal ordering. The presentist, however, is forced to either retreat back to anti-realism, saying that truths about the past just are the distributional properties even if they just came about, or abandon present-exclusive ontology.

The Last Thursdayism worry, at its core, is that even though the present has something pointing at last Wednesday, it was never the case that anything before last Thursday can lay claim to having had the privilege of being present. Cameron can still insist that, no, if an object just came into existence it cannot have distributional properties extending beyond its genesis. Since its genesis is already past and no longer exists, I do not see why not; not without a much more thorough account of what they are. I know they are not the four-dimensional shape of a spacetime worm, I know they are not complex conjunctive properties, and I know they are fundamental and irreducible, but beyond that I cannot see how they work. How exactly do they get from existing solely at the present to saying about an object how it is across a period of time? If the answer is ‘they just do fundamentally’ then how is that different from rejecting truthmaking and backing primitive past-facts or primitive past-properties?

Since Last Thursdayism bears similarities to other fanciful counter-examples – zombies in philosophy of mind and Cartesian demons in epistemology – I propose, for future investigations, that the presentist look in the literature of those dialectics for a defeater of the objection.

I have argued that presentist truthmaking cannot escape the Le Poidevin-Russell prong without lapsing into anti-realism, abandoning present-exclusive ontology, or resorting to primitives, since Last Thursdayism arises as a consequence of a privileged present and not of any particular truthmaking theory. I have argued that Cameron truthmaking initially fares well against the prong but ultimately either falls short against Last Thursdayism or is in need of a more thorough account of its distributional properties.


In my essay ‘Spacetime Worms‘ I gave presentist undertermination of the past uncharitably short thrift. This essay is my attempt to make up for that.




Share and Enjoy:
  • Facebook
  • Twitter
  • Digg
  • StumbleUpon
  • Reddit

Leave a Reply