containing a colourless liquid, and that each thinks a thought they would
express with the words, ‘There is still some water left in that glass’, and
consequently lifts the glass to drink from it. Since the behaviour is the same
in each case, we might think that the explanations we advance of that
behaviour should be the same too – which meansnotindividuating the
thoughts in terms of the inner structure of the natural kinds in question,
but rather narrowly, independently of the actual environment.
Of course the background principle appealed to here is not a hard-and-
fast one. For we know that there can be cases of convergent causation.
That is, there can be cases where instances of the very same event-types are
caused by quite diVerent routes. This is especially familiar in the case of
human action, since examples where people behave similarly but for very
diVerent reasons are rife. Thus, consider the variety of reasons people
might have for writing to apply for a particular job – one because he needs
a job, and any job would do; another because she wants that particular job;
another because he wants to please his mother; and so on. Yet the behav-
iour in each case is of an identical type (in some respects).
All the same, whenever two systems are changing and evolving in such a
way as to follow exactly similar trajectories, we surely have powerful
reason to believe that the underlying causal processes must be the same.
Thus imagine two ropes being tested in a company’s testing laboratory:
each begins to fray in the same place after exactly the same amount of time,
and then each snaps in the same place, again at the same time. Surely these
facts would give us reason to believe that the intrinsic properties of the two
ropes were the same, and that they were subjected to the same forces
throughout. Otherwise we would have to believe that the similar eVects
were a mere coincidence. Moreover, the more complex the eVects in a pair
of parallel sequences, the more unlikely the coincidence. And remember
that in the Twin Earth examples,allthe behaviours of the two Peters are
the same over anindeWnitetime-span!
There is an obvious reply that defenders of wide content can make to the
above argument. They can deny that thebehavioursof Petereand Petertw
are the same (under an intentional description). And if they do not really
behave in the same way, then there need be no presumption that their
behaviours should be caused by thoughts of identical types. Thus, consider
what it is that they do when they lift and drink from the glass: while Petere
drinkswater(H 2 O), Petertwdrinkstwater(XYZ). And these can be coun-
ted as belonging to two diVerent action-types. So it can, in eVect, be
objected that the argument above presupposes content-neutral (non-inten-
tionally described) descriptions of behaviour – arm-movings, glass-liftings,
and so on, but not water/twater-drinkings. In which case that argument
seems just to beg the question at issue. For if thoughts are widely in-
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