What are the key differences between (classical) pragmatism and conventionalism? I'm reasonably familiar with the first, and have just become aware of the second via a reference to Henri Poincaré's La Science et l'Hypothèse. From my current perspective the two doctrines appear at least broadly similar.
Here is a quote from Charles Sander Peirce on pragmatism:
Consider what effects, which might conceivably have practical bearings, we conceive the object of our conception to have. Then, our conception of those effects is the whole of our conception of the object.
And here is Wikipedia on conventionalism:
Conventionalism is the philosophical attitude that fundamental principles of a certain kind are grounded on (explicit or implicit) agreements in society, rather than on external reality.
Both descriptions refer to the practice of human discourse ("practical bearings", "agreements in society") rather than any metaphysical objects, hence the (perhaps) considerable similarity. There are some obvious differences around histories (U.S. vs. France, philosophy of religion in the case of William James vs. natural sciences, individual vs. societal dimension), but I'm mainly interested in (other) epistemological key differences here. I have already checked e.g. SEP, which does seem to address the matter either.