In the same way, "all men are mortal" is unfalsifiable: even if someone is observed who has not died so far, he could still die in the next instant. By contrast, "all men are immortal," is falsifiable by the presentation of just one dead man.
P: All men are mortal.
is equivalent to
~P: No man is immortal.
So of course, "all men are immortal" is a different, but related statement. We seem to be able to logically assign truth values to all three. My first question is, how is falsifiability related to the logical possibility of assigning truth values?
To further illustrate, in economics, we make a distinction between positive and normative statements. Positive statements (facts) can have a truth value, normative statements (opinions) cannot. In other words, positive statements are propositions, normative statements are not. In order to illustrate the concept further, I've often employed falsifiability (testability). Facts are testable; opinions are not. So it seems, at the very least, that the universe of all propositions is a superset of falsifiable propositions.
Q: A is A. = ~Q: ~A is ~A.
This classic tautology doesn't seem falsifiable since it can never be shown to be false. That is, we can logically assign a truth value (always true) to the proposition Q, but it isn't falsifiable. However, the related statement
R: A is ~A.
is always false (a contradiction?). Is R a proposition? Is something that is never true falsifiable? If so, this seems to violate the notion that falsifiability has nothing to do with actual truth values, on the logical possibility of their assignment.
Where am I confused?