In the last MLE seminar of term we discussed some extracts from chapter 5 of Sider’s Four-dimensionalism. John and Frank moaned about the way Sider sets the debate up – John in particular was keen to emphasize that it’s possible for a three-dimensionalist to adopt eternalism and to assert the existence of temporal parts. His view is that there is no ‘endurance/perdurance’ or ‘3d/4d’ debate – what we actually have are four or five pretty much orthogonal debates, and a myriad of potentially defensible combinations of views.
We agreed that Sider’s argument against what he calls the ‘worm view’ in favour of his ‘stage view’ is pretty weak. The crucial example goes by analogy: imagine we have to cross a wiggly road several times, and wonder how many roads we have to cross. This is meant to be analogous to the problem of how to count people prior to personal fission. Lewis has a way of counting (‘tensed identity’, which counts shared worm-segments rather than total worms) which is meant to explain how there is a sense in which there is only one person present prior to fission, and a sense in which we have to cross multiple roads to get to our location even when those roads are segments of a larger road. Sometimes we count by tensed identity, sometimes by timeless identity. (For a vigorous contemporary defence of this view, see this paper by Saunders and Wallace.)
Sider’s claim is that we should reject Lewisian tensed identity, since (allegedly) the claim that we contextually switch between different ways of counting is undesirable and unmotivated. But Sider has to posit an equally undesirable switch between our referring to stages and our referring to worms to explain the same kind of phenomenon. His final view is an ‘ambiguity view’ on which context determines whether the reference of our terms are worms or stages – but we retain a single, tenseless, way of counting. But this switching of reference would have to be a fairly substantial piece of hidden semantic structure, and it’s not at all clear that it’s less problematic than Lewis’ multiple ways of counting.
The problem for Sider becomes vivid when we consider objects going out of existence. While Benazir Bhutto was alive, our talk about her (according to Sider) referred to the stage of her co-present with our utterance. But now that she’s been assassinated, our talk about her now refers to the whole spacetime worm of her life. Sider presumably wouldn’t want to say that, supposing that she died midway through an utterance of ours which refers to her twice, that the first occurrence refers to a stage and the second to a worm. But I’m not sure how he can easily avoid saying something problematic here. Sider concedes there is a worry:
Sentences involving counting of the non-timeless variety, for example ‘there is one person in the room with me now’, receive a stage-theoretic analysis, as do certain sentences to be discussed below, since this analysis makes the best sense of our intuitions about those sentences. But in cases like that of timeless counting, a worm-theoretic analysis seems required. The concession perhaps makes the stage view a little less attractive since, arguably, candidate semantics that postulate this sort of ambiguity or indeterminacy seem, other things being equal, weaker than candidates that do not. Nevertheless, the stage view’s advantages outweigh this defect.
There is just no argument given for the final claim, that this defect is less problematic than the Lewisian ‘two kinds of counting’ story. Sider argues that ‘the evidence doesn’t require Lewis’ explanation’ – but it does require it if we wish to avoid an ambiguity in the semantics at the level of reference. At best, there is a stand-off between Sider and Lewis here. Perhaps some input from empirical semantics would help resolve it?