Wolfgang Schwarz

Threats of Pluralism

Sometimes the best argument for a certain assumption is that it proves fruitful in various theoretical contexts: Why believe in a plurality of worlds? Because the hypothesis is serviceable in semantics, decision theory, theories of intentional content, the interpretation of modalities, the definition of supervenience, etc. -- and that is a reason to believe that it is true. Another example, again by Lewis, is the argument for universals, or at least for a fundamental distinction between natural and unnatural properties: the assumption is serviceable to account for objective similarity, the determinacy of meaning and translation, the interpretation of some quantified sentences, the analysis of natural laws, etc. Similar arguments can be put forward for the existence of temporal parts, states of affairs, events and numbers.

These arguments presuppose that it is really the very same assumption, rather than a diverse family of similar sounding assumptions, that does all the work it is supposed to do. The case for numbers would be much worse if lots of different arithmetics were 'indispensable' in different branches of science. The problem is quite obvious for events: the events employed in relativity theory can hardly do as the events used in Davidsonian interpretations of English adverbs.

More interesting is the question of whether different kinds of universals are required to do all the new work for a theory of universals: Can the objects of nominalistically recalcitrant quantification be used to account for objective similarity? Even more interesting: is the naturalness needed to remove indeterminacy of reference the same as the naturalness of fundamental physical properties mentioned in laws of nature? Here is an argument, stolen from Karl Schafer, that they are not:

Suppose there is a community whose members have a sense organ for a quite unnatural property P. They also have a predicate W which they apply to certain things, all of which fall under P. But, as P is quite unnatural, all these things also fall under a more natural property Q, which is explicable only in microphysical terms of which the members of the community know nothing and which they can't detect at all. Now doesn't W denote P rather than Q?

The answer, I think, goes somehow like this: If W denotes P rather than Q then this is because some kind of response-dependence is part of its theoretical role: By linguitic convention, x is W iff x is classified as W by normal people under normal circumstances, or iff it appears to the speaker in a certain way. P satisfies this condition, but Q doen't. So Q isn't even a candidate for reference and therefore can't trump P. Of course, this response only works if linguistic conventions manage to yield the response-dependent theoretical role. I don't see any good reason though why they can't.

Another open question is whether different kinds of possible worlds are required to do all the work for modal realism (or ersatzism or fictionalism). The coherence of non-reductive ('type-B') physicalism depends on this question: Non-reductive physicalists agree that we can't rule out a priori the possibility of a zombie world, but they also claim that, as a matter of fact, there is no such possibility. Hence what we can't rule out it is not really a possibility. Perhaps it is nothing at all. Perhaps what we can't rule out is just the truth of a string of symbols or of a structured proposition, and this doesn't mean that there is some thing we can't rule out (as being actual). But the assumption that there are such things proves very useful in theories of intentionality, in information theory and in semantics. So the non-reductive physicalist should agree that there are these things, 'quasi-possible worlds' or however we may call them, but that they are not the same things called 'possible worlds' in the analysis of modal statements.

Again, the best answer is to show that all alleged examples supporting a plurality of kinds of worlds can be explained away (plus maybe to show that the plurality leads to an inelegant overall theory and a muddled modal epistemology). Unfortunately this doesn't help at all if the opponent finds modal pluralism independently plausible. I've met some people who strongly intuit that the realm of metaphysical possibility is quite independent of our concepts and of what we happen to know a priori. They say, for example, that this table could not be made of ice, and that we know that not by investigating into our use of "table" and the physics of the table, not even by semantic intuition, but by something completely different called 'modal intuition'. Moreover, and this is crucial, they say that the modal intuition faculty is irremediately fallible. Thus it happens that a statement is not verified by any possible situation (i.e. it is true at no possible world considered as actual) even though we fail to intuit that this is so, and no amount of information about the actual world can help us. I believe that this position rests on a confusion between modality and actuality: usually if something exists, it could just as well have failed to exist. Thus we have to make empirical observations to find out whether it does or doesn't exist. But this doesn't apply to possible worlds. It couldn't have happened that there is no world containing blue swans, or no world verifying "there are zombies". We don't need empirical observations or modal intuitions to rule out the possibility that these worlds fail to exist simply because there is no such possibility. No doubt this won't persuade the skeptic.

How bad is it that arguments against pluralism can always be blocked simply by intuitions to the contrary? Not very bad. For the same holds for all arguments. If you strongly intuit that there are true contradictions or monsters in Loch Ness, all available counter-evidence and counter-arguments will seem inconclusive and question-begging. So what?