There were two neat talks about Carnap at the MWPM conference this weekend, which got me thinking. I like Carnap, I like realism (well, more like, I don't understand anti-realism) so I like to try to give a realist reading to all Carnap's stuff about the principle of tolerance. But my current best realist Carnap also seems kindof trivial.
1. You can state truths in different languages, even languages which give different definitions/meanings to the same string of letters e.g. "atom".
2. Sometimes if you disagree with someone about "Xhood" (e.g. if you disagree about the question "viruses alive?") you can step back and use other facts that you agree on to characterize the situation, (e.g. viruses reproduce themselves in such and such a way, when they are dormant they don't do so and so, if we stipulate that something is alive iff it Xs then we will get the consequence that all physical things count as being alive) and decide what kind of stipulative definition of "alive" would be most useful to use in this context. Then you just go forward, using the word "alive" in this new sense, and not worrying about whether it was the same as what either of you originally meant by "alive".
Doing this lets you go on with biology without getting bogged down in likely unresolvable questions about whether viruses are alive.
BUT sometimes no stipulative definition given to a term will be as interesting as the one you started with (e.g. if you tried to re-stipulate the meaning of mathematical terms to avoid controversy about whether "there are infinitely many twin primes").
AND sometimes you disagree with your opponents so much about math/logic, that you can't agree with them about what the consequences of a given stipulation would be.