of course then you have to define what a 'lie' is without recourse to a definition of 'truth'.

Well, you are just saying that truth is everything that isn't non-truth, which is circular, and as you said, even if it's a good definiton, you would need to define "lie" without using the term "truth". How would you do it?

In the context of subjectivity, what is not a lie is not then the truth. I also think I would not define lie in a way which meant that which is not a lie is then truth in any context.

rather than try to define truth directly I think a definition could be base upon non-truth.
Filter out any and all significant lies, and what you are left with is truth.. — wax

Say that it's true that the Mississippi River is 2,320 miles long. That implies that it's false that the Missippi River is less than 1,000 miles long.

Let's say that Bob believes that the Mississippi River isn't over 1,000 miles long. Given that, if Bob says that the Mississippi River is over 1,000 miles long, Bob is lying. If Bob says that the Mississippi River isn't over 1,000 miles long, then Bob is being honest.

Honesty versus dishonesty (lying) is a matter of whether someone is telling us what they believe to be true. We don't have an additional requirement that what they believe to be true actually is true. It's enough, to be honest, that you tell us what you really believe. People aren't guilty of perjury in court if they tell us what they believe, but what they believe is mistaken. They're guilty of perjury if they tell us something other than what they believe, and we have evidence that they believe different than what their testimony was.

So getting rid of lies doesn't capture what is true. It just restricts us to what people really believe, but people can be in error.

Within the context of possible experience......

Empirical truth: that of which the negation is impossible.
Logical truth: that of which the negation is contradictory.

You could say:

A fact is a state of affairs.

....or a fact is a relation among things.

You could say that a proposition is something that (before we know if it's a fact) might be a fact, &/or something that purports to be a fact.

...or a proposition is something that has truth-value (or undetermined truth-value)

A proposition is true (has affirmative truth-value) if it's a fact.

Truth is the property of being true or having affirmative truth-value..

(These are what occur to me now, but I don't know how good they are.)

...or:

Within the context of possible experience......

Empirical truth: that of which the negation is impossible. — Mww

...or seemingly impossible?

Logical truth: that of which the negation is contradictory.

The proposition's negation implies a contradiction?

Michael Ossipoff

10 Tu

You can have true all day long. This is true; that is true; over there isn't true, and so forth. But you cannot have a rigorous definition of truth and that is a consequence of Godel's theorem. Godel, because truth isn't recursively definable, was forced back to the idea of provability, which is. Godel's undecidable proposition was such that by ordinary mathematical means neither could it be proved nor disproved. But because the proposition asserted its own unprovability, it was by provable by metamathematical reasoning. That is, there exists in mathematics a proposition that is both true and not mathematically provable. Had Godel found a rigorous - recursive - definition of truth, then by the same argument he would have a proposition not that was unprovable but true, but untrue, but true. Not good for mathematics, or anyone else.