Lewis on magnetism: Reply to Janssen-Lauret and Macbride
In my 2014 paper "Against Magnetism", I argued that the meta-semantics Lewis defended in "Putnam's Paradox" and pp.45-49 of "New Work" is (a) unattractive, (b) does not fit what Lewis wrote about meta-semantics elsewhere, and (c) was never Lewis's considered view.
In a paper forthcoming in the AJP, Frederique Janssen-Lauret and Fraser Macbride (henceforth, JL&M) disagree with my point (b), and present what they call "decisive evidence" against (c). Here's my response. In short, I'm not convinced.
Let's review some background. In "Putnam's Paradox" and pp.45-49 of "New Work", Lewis defends a theory I'll call Magnetised Global Descriptivism, or MGD for short. MGD is a theory of how words get their meaning. According to MGD, the correct interpretation of a language is the one that strikes the best balance between two desiderata: (1) making the sentences that are accepted by the speakers true (alternatively, the sentences that would be accepted in some kind of limit of enquiry), and (2) assigning objectively natural referents to the language's non-logical terms.
Let me go through the three reasons I offered (in "Against Magnetism") for thinking that Lewis did not endorse MGD, and comment on what JL&M say about them.
Obvious faults. I find MGD highly unattractive, and mentioned several problems with it in my paper. The problems are rather obvious, and surely didn't (all) escape Lewis. JL&M don't address any of them. Presumably they don't agree these problems would have stopped Lewis from accepting the theory. I think they would, but I won't go through all of them again. But I'll mention one, because Lewis also mentions it, and his response is instructive. The problem is that MGD is a non-starter unless we hold fixed the meaning of logical vocabulary (and the rules of compositional semantics). An urgent task for anyone who endorses MGD is therefore to explain how the meaning of logical vocabulary is determined -- that is, why logical vocabulary can be treated as "old vocabulary". Lewis has the following to say about this.
...perhaps the old vocabulary is just the first-order logical vocabulary. Putnam seems to assume this, but without telling us why that vocabulary is special, or how it got its reference. [p.224]
...the applicability of the model theory depends on treating exactly the first-order logical vocabulary as 'old' language, with antecedently determinate reference. As Robert Farrell has emphasised, Putnam has no right to give this vocabulary special treatment. Perhaps he only did it for the sake of the argument, giving away points just because he would not need them. [p.230]
To me, these passages strongly suggest that Lewis didn't see the problem as a challenge to his own view. That would be strange if Lewis endorsed MGD, as JL&M claim.
Lack of fit. Lewis wrote a lot about how natural languages get their meaning. Among other things, his PhD thesis and first book were on that topic. The answer he gave everywhere except in "Putnam's Paradox" and pp.45-59 of "New Work" is not MGD. Rather, Lewis suggested that the interpretation of natural languages is determined by conventions of use, which in turn boil down to certain beliefs and expectations in the relevant community. Once the beliefs and expectations are fixed, the interpretation of the language is fixed as well (to the extent that it is). Lewis also had an account of what determines the content of beliefs and expectations; that account looks even less like MGD, for Lewis didn't believe in a language of thought whose sentences could constitute a speaker's "total theory" and whose non-logical terms would stand in need of interpretation.
What do JL&M say about this lack of fit? They deny it. They don't even see a tension. I thought that I had explained in detail how MGD contradicts what Lewis wrote elsewhere about language, but apparently the message didn't come across. "Schwarz doesn't explain the alleged contradiction", JL&M say. As a reminder, here are three points of contradiction. (There are many more.)
- MGD assigns no role to the conventions that ground linguistic meaning on Lewis's own account.
- MGD makes meanings objectionably intransparent to competent users, in a way that goes against the central point of semantics, to explain and systematise linguistic behaviour.
- MGD only gives sensible results for expressively rich languages, and only if we hold fixed the meaning of logical expressions and the rules of compositional semantics. Lewis's own account has none of these limitations.
JL&M argue that far from contradicting Lewis's other writings on language, MGD nicely complements it. The idea is that Lewis's earlier writings only explained how entire sentences get their truth-conditions; they don't explain how individual words get their reference. That's the gap MGD is supposed to fill:
Because early Lewis only discussed the truth-conditions of sentences, and admitted he lacked an account of reference, it's difficult to see how the account of reference in 'Putnam's Paradox', magnetized global descriptivism, can 'contradict', as Schwarz claims, what Lewis wrote elsewhere on language.
Lewis's proposal [...] in 'Putnam’s Paradox' doesn’t conflict with what he'd written before. Appeal to making ideal theory come true supplements his earlier account, which had gone no further than assigning truth-conditions: choose an assignment of reference that makes ideal theory come out true relative to the assignment of conventionally established truth-conditions.
I don't understand this proposal. The supposed combination of views would be coherent if truth-conditions and reference were entirely independent. One could then tell one story about truth-conditions, and an entirely different story about reference. But that's surely implausible. In any case, MGD is not just a theory of reference. The interpretation it singles out as correct is supposed to tell us what the sentences of a language mean, not just what the individual words refer to. (Remember we need to hold fixed the meaning of the logical expressions and the compositional semantics for MGD to get off the ground.)
Here's what JL&M might have in mind: Lewis's earlier account of language did not fix the meanings of subsentential expressions; the conventions Lewis identifies as determining the truth-conditions of sentences are compatible with many assignments of meanings to subsentential expressions. What Lewis then came to accept is that the true meanings of subsentential expressions are the most natural ones among the various candidates.
That's a coherent view. (I mentioned it in my paper.) But it's not MGD. It has traded Global Descriptivism as a theory of how sentences get their truth-conditions for Lewis's convention-based account. And it has reduced the role of naturalness to breaking ties between different grammars producing the same truth-conditions. In my paper, I had set aside this view as uninteresting and unmotivated. I stand by these judgements. Why would one want subsentential semantic values to be objectively natural, rather than, say, simple to manipulate in linguistic theorising? What problem would that solve? Recall also that Lewis is explicit that subsentential semantic values are not referents, but more complex set-theoretic constructions.
The proposed view also doesn't make much sense of "Putnam's Paradox". Putnam's paradox is not about reference or subsentential semantic values. The paradox Lewis tries to dissolve is Putnam's claim that our total theory cannot possibly be false. This is a claim about the truth-values of sentences, not about subsentential semantic values. The naturalness constraint on meanings is supposed to force some sentences to become false that would otherwise have come out true.
To sum up:
- MGD is not just a theory of how subsentential expressions get their meaning. It is also a theory of how sentences get their meaning.
- This theory is markedly different from the theory Lewis defended elsewhere.
- One could coherently combine Lewis's convention-based metasemantics with a naturalness constraint on subsentential semantic values, but this is not what Lewis defends in "Putnam's Paradox" (or pp.45-49 of "New Work"), and there is no other reason to think it was Lewis's view.
The distancing. In both papers in which Lewis defends MGD, the defence is accompanied by a caveat. Here is the caveat in "Putnam's Paradox" [p.222]:
I shall acquiesce in Putnam's linguistic turn: I shall discuss the semantic interpretation of language rather than the assignment of content to attitudes, thus ignoring the possibility that the latter settles the former. It would be better, I think, to start with the attitudes and go on to language. But I think that would relocate, rather than avoid, the problem; wherefore I may as well discuss it on Putnam's own terms. [Footnote: For a discussion o f the 'relocated' problem and its solution, see the final section of my 'New Work for a Theory of Universals']
Here is the corresponding passage in "New Work":
You might well protest that Putnam's problem is misconceived, wherefore no need has been demonstrated for resources to solve it. Putnam seems to conceive of language entirely as a repository of theory, and not at all as a practice of social interaction. We have the language of the encyclopedia, but where is the language of the pub? Where are the communicative intentions and the mutual expectations that seem to have so much to do with what we mean? In fact, where is thought? It seems to enter the picture, if at all, only as the special case where the language to be interpreted is hard-wired, unspoken, hidden, and all too conjectural. I think the point is well taken, but I think it doesn't matter. If the problem of intentionality is rightly posed there will still be a threat of radical indeterminacy, there will still be a need for saving constraints, there will still be a remedy analogous to Merrill's suggested answer to Putnam, and there will still be a need for natural properties. Set language aside and consider instead the interpretation of thought...
What follows is a lengthy discussion of how mental states get their content. Nothing remotely like MGD figures in that discussion.
To me, these passages clearly indicate that Lewis disagreed with a presupposition of Putnam's Paradox: that the correct interpretation of a language is determined by what makes total theory come out true (Global Descriptivism, understood as a metasemantics), rather than by the attitudes in the relevant linguistic community. Both passages also explain why Lewis nonetheless goes on to address Putnam's paradox on Putnam's own terms: he thinks a somewhat analogous problem arises in his own account of how mental states get their content, and that appealing to objective naturalness helps with that problem.
What do JL&M say about these passages? According to JL&M,
Lewis meant what he said in 'Putnam's Paradox'. He was a global descriptivist who adopted reference magnetism to fend off radical indeterminacy of reference, modulo the caveat that content magnetism is first required to fend off radical indeterminacy of content at the level of thought.
In the remainder of JL&M's paper, the caveat is ignored altogether. So JL&M seem to interpret Lewis as saying that objective naturalness is needed not only in the correct theory of how words get their meaning, but also (and "first") in the correct theory of how mental states get their content. Surely this is not what Lewis is saying in the passages just quoted.
Interlude. I claim that in "Putnam's Paradox", Lewis defended a theory (namely MGD) which he didn't actually endorse. JL&M find this unbelievable. Why would Lewis defend a particular answer to a puzzle if he thought the correct answer is completely different?
Well, I said something about this, but apparently I didn't say it clearly enough. Here is what I think was going on.
To begin, Lewis was responding to a puzzle raised by Putnam. The puzzle presupposes a certain view of how words get their meaning. Lewis rejected that view. But he thought that given the presuppositions of Putnam's paradox, MGD is a good response. So on my interpretation, Lewis accepted MGD as a good response to Putnam's paradox, given the terms of the paradox.
Still, why would Lewis give this response, rather than point out that the presuppositions are mistaken? For two reasons.
First, as his says himself, he thought a somewhat analogous puzzle arises in his own account of how mental states get their content, which in turn affects how words get their content. And he liked a somewhat analogous solution to that puzzle.
(But it's important not to overstate the analogies. For example, the puzzle that arises for Lewis's theory of intentionality has nothing to do with reference. The decision-theoretic permutation argument Lewis gives in "New Work" vaguely resembles familiar permutation arguments for the indeterminacy of reference, but what is being permuted in Lewis's argument are assignments of propositional attitudes, not assignments of referents.)
Second, Lewis plausibly regarded Putnam's Global Descriptivism as a crude approximation to his own meta-semantics. The approximation simplifies the attitudes that ground meanings to just one: acceptance of a sentence. On Lewis's own account, any sentence that is widely accepted in a community is likely to be true (on the correct interpretation of the sentence). So if we had to work with the simplified basis of which sentences are accepted, a natural way to fill in the story is to say that the correct interpretation should, as much as possible, make the accepted sentences come out true.
Moreover, since Lewis accepted that objective naturalness plays a role in determining the content of attitudes, which in turn determine the interpretation of language, he also accepted that objective naturalness (indirectly) constrains the interpretation of language. Indeed, I suspect he thought that 'the sky is blue' means that the sky is blue partly in virtue of the fact that blue is more natural than grue. Not because there is a direct naturalness constraint on referents, but indirectly via the interpretation of the attitudes that give the sentence its meaning. (I speculate a bit about how this indirect route might go in my paper. It's far from obvious, especially because Lewis says so little about how exactly the naturalness of certain properties is meant to constrain the probability and utility functions that give content to our mental states.)
I mention all this because JL&M assume that on my interpretation, Lewis should reject MGD whenever he discusses Putnam's paradox in correspondence. They go on to cite various passages from letters in which Lewis doesn't do that, and treat that as "decisive evidence" against my interpretation.
Evidence from correspondence. I won't go through all the letters cited by JL&M. I don't think any of them undermines my interpretation of Lewis. Some of them seem completely irrelevant, such as this passage from a letter to Teller:
I'm not sure what you’re proposing. It might be this: (1) that imperfect naturalness of some properties is to be understood in terms of definability from perfectly natural properties; then for words to have imperfectly natural referents is the same as for them to be definable from words, if such there be, with perfectly natural referents. ... (1) is fine with me; it makes explicit something I've supposed, but left out because I didn't have details -- a theory of simplicity of definitions -- to offer.
So Lewis is "fine" with the idea that imperfect naturalness can be understood in terms of definability from perfect naturalness. I have no idea how that is meant to show that Lewis endorsed MGD.
In other letters, Lewis explicitly discusses Putnam's argument, and suggests, for example, that inegalitarianism about properties "would provide the necessary constraints on reference" to escape the paradoxical conclusion. I don't see why Lewis shouldn't have said that. On my interpretation, this is precisely what Lewis thought, although he also thought that Putnam's argument rests on an oversimplified metasemantics.
In a 2001 letter which may or may not be about Putnam's argument, Lewis states that "[f]airly determinate content of thought (or language) ... requires reference magnetism". Again, this is perfectly compatible with my interpretation of Lewis's views. Yes, Lewis did think that the content of our attitudes, and indirectly the content of our language, is partly fixed by constraints of objective naturalness. Admittedly, "reference magnetism" is a somewhat misleading label for the ideas presented in "New Work" from page 50 onwards, which describe how naturalness enters into the determination of mental content. So one might take Lewis's use of that label to suggest that he later switched to a completely different account on which the content of mental states is determined by assigning referents to mentalese words. But that would be a big change of opinion. I'd need to see a lot more evidence for it.
JL&M also cite a letter to Forrest from 1988, which actually supports my interpretation. The topic of the letter is Putnam's argument. Lewis writes:
Once the over gruesome interpretations are out by inegalitarianism, I would hope that fit can do the rest of the job. Fit is something like making ideal theory come true. I'm not sure how much farther we can go while joining Putnam in ignoring the difference between interpreting thought and interpreting language.
Overall, I don't find anything in JL&M's paper that really challenges the interpretation I offered in "Against Magnetism".
PS. The strongest piece of evidence against my interpretation that I know of is something JL&M don't mention: footnote 6 of "Many but Almost One". Here Lewis discusses the problem that in the vicinity of any cat there are countless aggregates of matter that equally deserve the name 'cat'. He adds:
I do not think reference is entirely up to our choice. Some things are by their nature more eligible than others to be referents or objects of thought, and when we do nothing to settle the contest in favour of the less eligible, then the more eligible wins by default; see Lewis (1984) [i.e., "Putnam's Paradox"].
I mention this passage in footnote 7 of "Against Magnetism", but falsely claim that it is only about thought. (I'm not sure how that happened. Maybe I parsed "referents or objects of thought" as "referents of thought or objects of thought"? That's grammatically possible, but I don't think it's what Lewis had in mind.)
I'm not entirely sure what to make of this passage. As I said, I think it's the strongest piece of evidence against my interpretation of Lewis. But it's far from conclusive, especially given that every alternative interpretation I can think of (such as the interpretation defended by JL&M) clashes with much more of Lewis's writings, besides attributing views to him that have obvious and serious faults.
Also, as I said earlier, Lewis may well have thought the upshot of his complicated and indirect metasemantics is a kind of reference magnetism that resembles MGD, but without running into all the problems for MGD that I raised in my paper. That is, for all I'm suggesting, Lewis may well have thought that 'blue' means blue partly in virtue of the objective naturalness of blue, but not because there's a brute naturalness constraint on the reference of words. The true story is much more complicated, and wouldn't fit in a footnote.