I agree with your explanation of the intended semantics of the sentence, which is also my explanation. What I disagree with is the suggestion that we denote that meaning using “Let us sign this treaty.” instead of “We should sign this treaty.” I believe the intended meaning is more naturally expressed using the second sentence, and trying to redefine the word “should” so that the second sentence means something else and we’re forced to use the first sentence to express the same meaning, is wrong.
Also, since the first sentence is imperative instead of declarative, I’m not sure that it doesn’t mean something else already, so that now you’re hijacking two words instead of one.
There can be a separable sense of “should” that indicates rationality. Thus, “we should sign the treaty” can be an interesting truth for both parties when the “should” is that of rationality, and true for both parties but only interesting from the human side when the “should” is a moral should.
This commits one to what philosophers call moral externalism, namely, the view that what is morally required is not necessarily rationally required. Which is not a reason to reject the view, but I expect it will be criticized.
I agree with your explanation of the intended semantics of the sentence, which is also my explanation. What I disagree with is the suggestion that we denote that meaning using “Let us sign this treaty.” instead of “We should sign this treaty.” I believe the intended meaning is more naturally expressed using the second sentence, and trying to redefine the word “should” so that the second sentence means something else and we’re forced to use the first sentence to express the same meaning, is wrong.
Also, since the first sentence is imperative instead of declarative, I’m not sure that it doesn’t mean something else already, so that now you’re hijacking two words instead of one.
There can be a separable sense of “should” that indicates rationality. Thus, “we should sign the treaty” can be an interesting truth for both parties when the “should” is that of rationality, and true for both parties but only interesting from the human side when the “should” is a moral should.
This commits one to what philosophers call moral externalism, namely, the view that what is morally required is not necessarily rationally required. Which is not a reason to reject the view, but I expect it will be criticized.