Right, so you’d need a premise like “A given proposition can only have one truth value”. That’s not trivial though, and it’s been the subject of historical debate. For example, “Hen is sitting” is true...and false....and true again. You can work around that by saying “propositions come with time indexes” or something, but that’s far from trivial. Why can’t differences in speaker have the same effect?
So the SEP quote may be trivially false under a certain understanding of ‘proposition’ but I take it the issue of how to understand propositions is part of what the SEP quote intends to raise.
Right, so you’d need a premise like “A given proposition can only have one truth value”. That’s not trivial though, and it’s been the subject of historical debate. For example, “Hen is sitting” is true...and false....and true again. You can work around that by saying “propositions come with time indexes” or something, but that’s far from trivial. Why can’t differences in speaker have the same effect?
So the SEP quote may be trivially false under a certain understanding of ‘proposition’ but I take it the issue of how to understand propositions is part of what the SEP quote intends to raise.