David Lewis: Notes & Abstracts

Convention: A Philosophical Study

Social conventions are analysed, roughly, as regularities in their solution of recurrent coordination problems -- situations of interdependent decision in which common interest predominates. An example is our [Americans', etc.] regularity of driving on the right: each does so to coordinate with his fellow drivers, but we would have been just as well off to coordinate by all driving on the left. Other examples are discussed; conventions are contrasted with other sorts of regularity; conventions governing systems of communication are singled out for special attention. It is shown that the latter can be described as conventions to be truthful with respect to a particular assignment of truth conditions to sentences or other units of communication.



A counterfactual conditional has the form: if it were that A, then it would be that B (where A is usually assumed false). What does this mean? Roughly: in certain possible worlds where A holds, B holds also. But which A-worlds should we consider? Not all; those that differ gratuitously from our actual world should be ignored. Not those that differ from our world only in that A holds; for no two worlds can differ in one respect only. Rather, we should consider the A-worlds most similar, overall, to our world. If there are no most similar A-worlds, then we should consider whether some A-world where B holds is more similar to ours than any where B does not hold.
An analysis of counterfactuals is given along these lines. It is shown to admit of various formulations. It is compared with other theories of counterfactuals. Its foundations, in comparative similarity of possible worlds, are defended. Analogies are drawn between counterfactuals, thus analysed, and other concepts. An axiomatic logic of counterfactuals is given.


On the Plurality of Worlds

We ought to believe in other possible worlds and individuals because systematic philosophy goes more smoothly in many ways if we do; the reason parallels the mathematicians' reason for believing in the set-theoretical universe. By "other worlds" I mean other things of a kind with the world we are part of: concrete particulars, unified by spatiotemporal unification or something analogous, sufficient in number and variety to satisfy a principle to the effect, roughly, that anything can coexist with anything. I answer objections claiming that such modal realism is trivially inconsistent, or leads to paradoxes akin to those of naive set theory, or undermines the possibility of modal knowledge, or leads to scepticism or indifference or a loss of the seeming arbitrariness of things. But I concede that its extreme disagreement with common opinion is a high price to pay for its advantages. I therefore consider various versions of ersatz modal realism, in which abstract representations are supposed to replace the other worlds; different versions suffer from different objections, and none is satisfactory. Finally, I consider the so-called problem of trans-world identity. I stress a distinction between the uncontroversial thesis that things exist according to many worlds and the very problematic thesis that things exist as part of many worlds.