Online Papers - Brian Weatherson

David Lewis 53
D. thesis, and published in 1969. The book was an extended response to the arguments
of Quine and others than language could not be conventional. Quine’s argument
was that conventions are agreements, and agreements require language, so language
must be prior to any convention, not a consequence of a convention. Lewis’s
response is to deny that conventions require anything like an agreement. Rather,
on his view, conventions are regularities in action that solve co-ordination problems.
We can stumble into such a regularity without ever agreeing to do so. And such a
regularity can persist simply because it is in everyone’s best interest that it persist.
2.1 Analysis of Convention
Lewis viewed conventions as solutions to co-ordination problems (see Section 3.2
of the entry on convention). His thinking about these problems was heavily influenced
by Thomas Schelling’s work on co-operative games in The Strategy of Conflict
(Schelling, 1960). Many of the key ideas in Lewis’s book come from game theory.
The simplest cases in which conventions arise are ones where we are repeatedly
playing a game that is purely co-operative, i.e. the payoffs to each agent are the same,
and there are multiple equilibria. In such a case, we may well hope for the equilibrium
to persist. At the very least, we will prefer the persistence of the equilibrium to any
one person deviating from it. And we will have this preference even if we would
prefer, all things considered, to be in some other equilibrium state. In such a case,
there may well be a practice of continuing to play one’s part in the equilibrium that
has been reached. This is a regularity in action—it involves making moves in the
repeated game. Given that everyone else is following the regularity, each agent has a
reason to follow the regularity; otherwise it wouldn’t be an equilibrium. But if other
agents acted differently, agents would not be interested in following the regularity,
since there are alternative equilibria. Because these three conditions are met, Lewis
argued that the practice is really a convention, even if there was never any explicit
agreement to continue it.
The case we started with was restricted in two important ways. First, the case
involved games that were perfectly repeated. Second, it involved games where the
payoffs were perfectly symmetric. Lewis’s theory of convention involved getting rid
of both restrictions.
Instead of focussing on repeated co-ordination problems, Lewis just focussed on
repeated situations which collectively constitute a co-ordination problem. Lewis does
not identify situations with games. A repeated situation may come in different ‘versions’,
each of which is represented by a different game. For example, it may be that
the costs of performing some kind of action differ on different occasions, so the formal
game will be different, but the differences are small enough that it makes sense
to have a common practice. And Lewis does not require that there be identity of
interests. In Convention he does require that there be large overlap of interests, but
this requirement does not do much work, and is abandoned in later writing. With
those requirements weakened, we get the following definition of convention.
A regularity R in the behaviour of members of a population P when they
are agents in a recurrent situation S is a convention if and only if it is true