Dimitri: So, Tasso, you seem to be one of those guys who thinks there is no absolute truth, that all truth is relative.
Tasso: Right.
Dimitri: Are you sure of that?
Tasso: Absolutely.
– Cathcart. T., Klein. D. 2007. Plato and a Platypus Walk into a Bar New York, United States: Penguin p. 179
Knowledge Guild 
It’s like “left” and “right”. Your right hand is always on your right and your left hand is always on your left, no matter where you look. So, left and right seem to be constant, unambiguous, absolute, and unchangeable.
How would you define an absolute truth?
Or everything has exceptions except the fact that everything has exceptions?
Often truth is a question of perspective. In a mirror, a left hand is a righthand one.
The definition has to be self-referring and trivial. Like “I am”, for example. Otherwise it will rely on something else and therefore will be relative. But self-referring definitions do not make much sense. So, it’s best to avoid them altogether, much like the definition of nothing or discussions of where everything came from. The statement “everything came from nothing” is an example of an absolute nonsense.
Often truth is a question of perspective.
Could be. But is that always the case?
Otherwise it will rely on something else and therefore will be relative.
If a truth relies on something else, does that make it relative? An empiricist might argue that everything needs to be observed in order for it to have a truth value. In view of that, where does that leave the term relative?
Empirical truth relies on observation. What about unobserved things? Can they not be true? Observation always alters the observed phenomena. In many cases, significantly. Chances are, in the absence of an observer things would look or behave quite differently. Observation has physical limitations. With a naked eye one would see something different than using an optical tool. There are many ways in which empirical truth can be called relative.
Empirical truth relies on observation. What about unobserved things? Can they not be true?
I agree. This leads to difficulties.
But what about the question “If a truth relies on something else, does that make it relative?”
I think so. Absolute truth can’t depend on anything. It must be founded on itself. Take the statement from above
It has to make a self-referring exception to avoid self-contradiction. But anyway, if you have an example of an absolute truth relying on something else, I’m interested to know.