ABSTRACT
The thought that theories are incommensurable is the thought that theories simply cannot be compared and consequently there cannot be any rationally justifiable reason for thinking that one theory is better than another. Expressed in this bold universal form, the thesis that theories are incommensurable is extremely implausible. This requires the caveat that it is implausible in so far as it is intelligible. Taken literally, it is implausible because it suggests that I could never have rationally justifiable grounds for holding any belief whatsoever, say, that I now see a typewriter, rather than a belief incompatible with it, say, that I do not see a typewriter. For if I could have grounds for rationally preferring one of those beliefs to the other why could I not have grounds for preferring one theory to another? That is, why should theories, as complex webs of beliefs, be any different from simple, humble everyday beliefs? The implausibility of this consequence or apparent consequence ought to prompt us to consider what motivates those who articulate the thesis of the incommensurability of theories. This is done below, for one presumes that they are not merely offering a thinly disguised version of traditional scepticism.
