Saturday 2 January 2016

The Humphrey Objection to Modal Realism

The Humphrey objection to modal realism, due to Kripke, centres on counterpart theory, and alleges that this assigns counterintuitive truth-conditions to modal statements about individuals. It is historically important, as Kripke made the objection in his influential Naming and Necessity lectures, long before Lewis published his full defence of modal realism in 1986.

Kripke put the objection as follows:

Thus if we say "Humphrey might have won the election (if only he had done such-and-such)”, we are not talking about something that might have happened to Humphrey but to someone else, a "counterpart". Probably, however, Humphrey could not care less whether someone else, no matter how much resembling him, would have been victorious in another possible world. Thus, Lewis's view seems to me even more bizarre than the usual notions of transworld identification that it replaces. (Kripke 1980:45 note 13.)

It is by now, I think, pretty widely accepted that Kripke, while he may have been on to something here, did not put the point optimally. To the objection put this way, there is a cogent response: it is not correct to say that, according to counterpart-theoretic modal realism, we 'are not talking about something that might have happened to Humphrey'. What counterpart-theoretic says is that talk about 'what might have happened to Humphrey' is to be analyzed in terms of what does happen to his counterparts in other worlds. So according to the counterpart-theoretic modal realist, when we say 'Humphrey might have won the election', we are indeed talking about what might have happened to Humphrey. Their characteristic claim is to add that this thing we're talking about is to be analyzed in terms of what happens to counterparts. (Lewis drives this point home in On the Plurality of Worlds.)

Similarly, the second part of Kripke's objection – that 'Humphrey could not care less whether someone else, no matter how much resembling him, would have been victorious in another possible world' – can be convincingly argued to miss the mark. The counterpart-theoretic modal realist can agree that Humphrey could not care less about this. For the way they analyze talk about whether 'someone else' (a counterpart) 'would have been victorious in another possible world' is in terms of counterparts of that someone else – counterparts of Humphrey's counterparts. And it is compatible with Humphrey not being interested in what happens to the counterparts of some one of his counterparts, that he be interested in something which – upon analysis – turns out to be a question of what happens to his own counterparts.

This last point may be a bit pedantic, however. What if we simply reform the second part of Kripke's objection by changing the 'would have been' to an 'is'? This yields: 'Humphrey could not care less whether someone else, no matter how much resembling him, is victorious in another possible world?'

This is better, but there is still a strong reply. As Sider says in his unpublished 'Beyond the Humphrey Objection', this is 'just the paradox of analysis':

A reasonable person can care about a property under one description (“possibly winning”) while not caring about the same property under another description (“having a counterpart who wins”), provided it is not obvious that the descriptions pick out the same property. Correct analyses need not be obvious to competent language users. Obviousness may count for something, but theoretical virtues are important as well in determining which analyses we ought to accept (p. 2)

I endorse this as a response to the version of the Humphrey objection just considered. However, I want presently to register a difference with Sider about whether this response also works for another version of the objection.

This other version puts aside what Humphrey cares about, and appeals directly to our intuitions. Sider puts this version of the objection as follows: 'Look, it is just obvious that possibly winning is not the same as having a counterpart who wins' (pp. 1 – 2) And the response quoted above is put forward by Sider as a response to both the previously considered version and this one. (He explicitly prefaces the passage with 'Reply to ii) and iii)' (p. 2).)

Does Sider's response apply here too? On reflection, I think clearly not. The response makes the point that a correct analysis need not be obvious (while granting that obviousness may count for something). But the present version of the objection is alleging, not that it isn't obvious, but that it is obviously not the case. Sider, in putting the passage in question forward as a response to this, is sliding from '(~p) is obvious' to '~(p is obvious)' and thus failing to address the objection.

So we seem to have a version of the Humphrey objection which is stronger than the others so far considered. But we can improve it further by getting away from obviousness altogether, which is a red herring. Saying that possibly winning is obviously not the same as having a winning counterpart risks being too strong. The rhetorically wise thing to do is tone it down, and simply enter a plea that it doesn't intuitively seem that possibly winning is the same as having a winning counterpart. Or putting the point semantically: the truth-condition Lewis assigns to 'Humphrey could have won' is counterintuitive.

So, despite the availability of strong responses to the original and certain subsequent versions of the Humphrey objection, the core point remains that the truth-condition assigned by Lewis is counterintuitive.

(Incidentally, Lewis suggested that forms of ersatzism are no better on this score: in that case, what “gets into the act” is not another person, but 'some abstract whatnot' (Lewis 1986, p. 194.) This isn't a strong reply to the objection, of course, as ersatzism is far from the only other game in town when it comes to the semantics of modal attributions such as 'Humphrey might have won'. Nevertheless and for what it's worth: perhaps an abstract whatnot getting into the act is, from an intuitive point of view, not quite as bad as another person getting into the act. Bringing in another person, it seems to me, feels more like crowding out Humphrey, more like putting something in his place.)

So, there is a version of the Humphrey objection which has some force. However, modal realism with overlap, in contrast to counterpart-theoretic modal realism a la Lewis, is immune to the Humphrey objection. Lewis wasn't swayed by this, since he had reasons to think modal realism with overlap unpalatable. Since then, advocates of overlap have, as might have been predicted, emerged (most notably McDaniel in his (2004), 'Modal Realism with Overlap').

It may be that the considerations against overlap are quite compelling, in which case these together with the Humphrey objection (once it is freed from its initial faulty formulation) have significant force against modal realism in general. However, I do not want to get deep into comparing the relative merits of counterpart-theoretic modal realism and modal realism with overlap, and would prefer to have an objection along similar lines which applies to both. Therefore, I advocate that we take the Humphrey objection, not just as a self-sufficient objection which affects the dominant form of modal realism but not modal realism with overlap, but also as a clue: modal realism – in both flavours – may be counterintuitive on the semantic front, and this may be a good reason to reject it. Since the Humphrey objection itself fails to apply to modal realism with overlap, we should set it aside and go on to try for a more general semantic objection. I hope to develop this in a future post.


Kripke, Saul A. (1980). Naming and Necessity. Harvard University Press.

Lewis, David K. (1986). On the Plurality of Worlds. Blackwell Publishers.

McDaniel, Kris (2004). Modal realism with overlap. Australasian Journal of Philosophy 82 (1):137 – 152.

Sider, Theodore. unpublished. Beyond the Humphrey Objection.

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