Can you expand on that? How do you have logical relationships among statements that don’t have truth-values?
If I think about it in abstract mathematical terms, just as a distance is a relationship between things (positions) that are not distances, one might set up a system in which implication is a truth-valued relationship between things that are not truth values, but I’ve never heard of such a system.
You can define a notion of logical consequence that isn’t preservation of truth and is therefore applicable to sentences that have no truth-values. For example, define a state as some sort of thing, define what it means for a sentence to be accepted in a state, and then define consequence as preservation of acceptance. But you still can’t identify acceptance with truth because you’ll have a separate notion of the truth which, in turn, is used in the definition of acceptance. It’s just that this notion of truth is only defined for some sentences of the language. (As a very simple case, say a state is a set of worlds, and a non-modal sentence φ is accepted in a state s iff φ is true in all worlds w in s.)
Mark Schröder and Seth Yalcin are two people on the philosophical side who defend modal expressivism with a semantics of that sort. On the more logico-linguistic side, there’s lots of Dutch people, for example Frank Veltman and Jeroen Groenendijk.
This depends on how you think about things (and what you count as a truth value), but arguably, ‘x = 3’ and ‘x² = 9’ do not have truth values, but ‘if x = 3, then x² = 9’ does.
Sure, that’s one way to look at it. And a function from values of x to truth values is not itself a truth value. You may say that a constant function from values of x to the value True is not itself a truth value either, but it’s much closer (after all, you know which one it would be if it were one), so it’s a minor shift to your way of looking at it to get what I said.
Now consider ‘If x² = 9, then x = 3’. A lot of people would naturally want to label that False (at least if they remember about negative numbers). As a function from values of x to truth values, this is not constant (and in fact it assigns True to every real value of x except one), so this is not even the same way of looking at things as in my previous paragraph. But it’s common.
So if you want implication between non-truth-values to be a truth value consistently, then this is how I would do it.
Can you expand on that? How do you have logical relationships among statements that don’t have truth-values?
If I think about it in abstract mathematical terms, just as a distance is a relationship between things (positions) that are not distances, one might set up a system in which implication is a truth-valued relationship between things that are not truth values, but I’ve never heard of such a system.
You can define a notion of logical consequence that isn’t preservation of truth and is therefore applicable to sentences that have no truth-values. For example, define a state as some sort of thing, define what it means for a sentence to be accepted in a state, and then define consequence as preservation of acceptance. But you still can’t identify acceptance with truth because you’ll have a separate notion of the truth which, in turn, is used in the definition of acceptance. It’s just that this notion of truth is only defined for some sentences of the language. (As a very simple case, say a state is a set of worlds, and a non-modal sentence φ is accepted in a state s iff φ is true in all worlds w in s.)
Mark Schröder and Seth Yalcin are two people on the philosophical side who defend modal expressivism with a semantics of that sort. On the more logico-linguistic side, there’s lots of Dutch people, for example Frank Veltman and Jeroen Groenendijk.
This depends on how you think about things (and what you count as a truth value), but arguably, ‘x = 3’ and ‘x² = 9’ do not have truth values, but ‘if x = 3, then x² = 9’ does.
I would say that “x=3” has a function from values of x to truth values, as does “if x = 3, then x² = 9″ (a constant function to the value “true”).
Sure, that’s one way to look at it. And a function from values of x to truth values is not itself a truth value. You may say that a constant function from values of x to the value True is not itself a truth value either, but it’s much closer (after all, you know which one it would be if it were one), so it’s a minor shift to your way of looking at it to get what I said.
Now consider ‘If x² = 9, then x = 3’. A lot of people would naturally want to label that False (at least if they remember about negative numbers). As a function from values of x to truth values, this is not constant (and in fact it assigns True to every real value of x except one), so this is not even the same way of looking at things as in my previous paragraph. But it’s common.
So if you want implication between non-truth-values to be a truth value consistently, then this is how I would do it.
That depends on the domain of x. That and the universal quantifier over its domain are typically omitted when they are clear from the context.
Yes, if we’re talking only about positive numbers, then ‘If x² = 9, then x = 3’ is true.