Anti-Individualism and Knowledge

Brown, Anti-Individualism and Knowledge

Why does Brown think there can be "no motivation" for the Fregean position of denying transparency of difference of sense but affirming transparency of sameness? You might think that transparency of sameness is a requirement for recognizing that inferences are valid at all, and that failure of transparency of difference is a feature of making inferences in a changing world.

What would happen if there was no transparency of sameness for sense? You couldn't immediately (without additional empirical information) know that two tokens co-referred (and not just demonstratives--names too). And one might wonder what the status of the empirical information would have in making an inference valid: wouldn't you need to know, of a premise linking the sense of one token with the sense of another, that its terms shared sense with the terms it was meant to link? It seems that without some transparency of sameness, there can be no such thing as a valid inference (in Campbell's neo-Fregean sense of validity: that is, knowing that an inference is valid so that it can extend our knowledge).

So it looks like there is some motivation for holding onto transparency of sameness while rejecting transparency of difference of sense.