Why are there so many different theories of truth in philosophy and does the concept of "truth" have a different meaning compared to how it is generally used by non-philosophers? "Truth" for us non-philosophers seems to denote that which is absolutely incontrovertible and not open to debate. As an example, for non-philosophers, it is the truth that JFK was shot on November 22, 1963; it is debatable as to exactly WHO shot him and HOW but there is no denying he was shot that day. So do philosophers agree that it is the truth that JFK was shot on that day or is even that open to interpretation using the multiple theories of truth out there and what does that even mean?

Perhaps so many philosophical theories of truth exist because the concept of truth is central and fundamental and because philosophers have been discussing it for such a long time. See the SEP entry on truth for a survey of various theories. As for non-philosophers, I doubt that they're as united in their view of truth as you suggest, and I doubt that they're united around the conception of truth that you proposed: "that which is absolutely incontrovertible and not open to debate." I've met many non-philosophers who claim that both sides in a debate can have the true answer to the precise issue being debated: my side of the debate can be true (for me), while your side can be true (for you). I don't accept their claim, but it certainly seems to be popular. And given how strange human beings often are, few if any statements are going to be "absolutely incontrovertible" if that means "beyond any possible controversy." If, instead, it means "not rationally deniable," then the controversy will...

who decides what is "true"? What if I believe that it's TRUE that Santa Claus exists? Wouldn't it be "true for me"?

I'm not sure how to interpret the quotation marks in your first question; I'll assume they're inessential. Who decides what's true? No one, as far as I can see. One can recognize what's true, discover what's true, conclude that such-and-such is true, etc. But I don't think any of that amounts to deciding what's true. I'm not sure that even the president genuinely decides that it's true that so-and-so is pardoned; I think he decides to declare that so-and-so is pardoned, and his declaration then makes it true that so-and-so is pardoned. But he doesn't decide that his declaration makes it true. I'm not sure how to interpret the capitalization in your second question; I'll assume it's inessential. If you believe that Santa Claus exists, then as far as you're concerned Santa Claus exists. If that's what you mean by "true for me," then it's just another way of saying that you believe that Santa Claus exists, which of course doesn't make your belief true. If it did, then the concept of a false...

What is the the truth value, if they have one, of propositions whose subject do not exist? "The current king of France is bald" is the famous example. Is that true or false, or neither? I have a hard time understanding how the current king of France can be neither bald nor not bald, even though I have no trouble understanding that there is no current king of France.

Philosophers have given various answers to questions like yours. See, for example, this SEP entry . Here's one approach: "The current king of France is bald" is false because it implies the existence of a current king of France when in fact there isn't one. "The current king of France is not bald" is likewise false if it's construed as implying the existence of a current king of France (and asserting of him that he's not bald). On a possible but perhaps less likely interpretation, the second quoted sentence is simply the wide-scope negation of the first quoted sentence: i.e., "It's false that the current king of France is bald." On that interpretation, the second quoted sentence comes out true since it simply asserts that the first quoted sentence is false. On neither interpretation is anyone neither bald nor not bald, so that particular claim of classical logic -- everything is either bald or not bald -- is preserved.

They say that relativism can not be affirmed without contradiction because to do so would imply that relativism had truth in an absolute sense. Is this simply an oversimplification or a strawman?

I suspect that one can affirm relativism without contradiction provided one is willing to embrace an endless regress . One can affirm the following statements: (R1) No statement is true except relative to some perspective (or worldview, or standard, or set of assumptions, or conceptual scheme). (R2) Statement R1 is true, but only relative to some perspective (or worldview, or standard, or set of assumptions, or conceptual scheme). (R3) Statement R2 is true, but only relative to some perspective (or worldview, or standard, or set of assumptions, or conceptual scheme). ...and so on without end. The endless regress allows one to postpone indefinitely any commitment to a non-relative truth. To be fair, however, one might wonder whether such a position has any cognitive content and, even if it does, whether our finite minds can truly understand such a position. For more, you might consult the detailed SEP entry on relativism available at this link .