Perhaps the thick presentist would be able to argue their way out of this tight spot. Perhaps the notion of an extended present – even if lacking proper parts – would give them sufficient resources to tell a story about biff relations holding over time within the present. But, even if such a case could be made, there is yet a further problem for the thick presentist in trying to respond to (B3).
(B3) claims that any perceptual awareness of extended events must be derivative if experiential states are momentary. Rejecting (B3) means that the presentist must hold that the event – the object of perception – is non-derivatively causally connected to the experiential state. Assuming there is no backwards causality in operation here, the experiential state will obtain at, or some short time after, the end of the event. We may say that the object of experience, event A, occurs from t1 to t3 – at which point experiential state B obtains. As discussed above, there must be a nonlocal causal relation that holds between A at t1 and B at t3. The presentist’s solution to trans-temporal biff relations considered above was to posit an extended present within which the relations can hold. To apply the same model here would means positing an extended present from t1 to t3. Why this is unacceptable becomes clear when we consider how long this interval must be.
The A-theorist’s argument from experience says, in effect, that because we have experiences as of A-change, we should conclude that A-change occurs in reality. The B- theorist’s counter-argument says that even if A-change events occur, we could only be derivatively aware of them – and these sorts of experiences cannot constitute veridical experiences as of A-change. The A-theorist says that we can be non-derivatively aware of events – specifically, A-change events. These are those putative A-theoretic events
such as movement.17 So in rejecting (B3), the A-theorist thinks we can be non-
derivatively aware of movement. Let’s spell out what this entails for the thick presentist. In chapter 3, if you recall, the idea of a ‘borderline motion experience’ was introduced. We have a borderline motion experience when we observe an object moving so slowly we are only just able to detect its movement. If the object was to move any slower we would not see it move. We imagined an hour hand so long that we could just about see its tip move. Let’s take this to be the event the presentist claims us to be non-derivatively aware of.
Over short enough timescales, the positions of the hour hand are indiscriminable; there is a minimum duration we would need to watch it for before we could perceive any change. Following Ian Phillips (2011a), a working estimate for this duration was put at 300ms. If we were to watch the hour hand for less than 300ms, we wouldn’t perceive a change. So the change we perceive occurs over 300ms or so. This, then, is the change event of which we are perceptually aware. Alarm bells should now be ringing for the presentist. We now have a timescale over which the nonlocal biff relations between the event and the mental state must hold. Event A, the change event in question, begins at t1 and ends at t3, which we are supposing to be 300ms later. Experiential state B must obtain no earlier than t3 if we are to rule out backwards causality. So there will be a nonlocal causal relation holding between t1 and t3, which is a temporal distance of 300ms. The presentist’s solution to the problem of trans-temporal causal relations is to posit an extended present within which the causal relata are encompassed. But on this model, the present must have an extension of at least 300ms! Moreover, it is obscure how the presentist could account for the fact that sensitivity to motion varies from perceiver to perceiver. If one person’s borderline motion experience takes 300ms, what do we make of someone else’s which takes 310ms? It is difficult to see how the presentist could maintain that the present has an objective duration.
Intuitive grotesqueness aside, we can labour the point by stating the obvious fact that things happen at sub-300ms intervals. It cannot therefore be the case that the proposed extended ‘present’ is mereologically simple. Hence, the Augustinian refutation will apply. Further, 300ms is nowhere near the proposals found in quantum physics, to which
17 In Chapter 3 is was suggested that what we regard as an experience of movement is in fact a
combination of (at least) two perceptual mechanisms – one that detects positional change and one that detects motion per se, or ‘pure’ motion.
the presentist might be tempted to appeal. Even if the 300ms estimate is out by an order of magnitude or more, the discrepancy would still be enormous (compared with the 10-44
to 10-24 second proposals in quantum physics). Positing an extended present just isn’t going to work for the presentist trying to accommodate our experience of A-change events. I conclude that if the A-theorist wants to reject (B3), they aren’t going to have much success from within the presentist camp.