"Well, it's nice that you believe that. I guess that's just what's true for you."
We've all at least heard of this phrase, if we haven't heard it specifically shot to us. In today's society, all the craze is that there is no absolute truth. Never mind that this statement is itself an absolute statement, and if true, is a form of absolute truth. As R.C. Sproul puts it in The Consequences of Ideas,
"Modern relativists...proclaim that there are no absolutes (except for the absolute that there are no absolutes!)."
This shocking paradox in and of itself proves that there has to be at least a little bit of absolute truth, but it would be a huge leap to say that this form of absolute truth is absolute, or in other words, that ALL truth is absolute.
It is impossible to prove either way whether all truth is absolute or not. This is part of the appeal that relativism has in society today. However, simply because a belief lacks proof, the opposite reasoning is not necessarily true. To me, it is far more logical to assume that there is a universal truth that exists than to assume otherwise.
For instance, if there is some truth that is absolute and others not, where is that line drawn? What elements of facts are absolute and which are subjective? It's hard to draw a line anywhere, but the ideas of preference. For instance, I may say that Three Musketeers is the best candy, and you may disagree and say that Snickers are better (as a side note, both are fantastic), but absent trolling, neither of us can dispute that they are both candies. In other words, how we react to and perceive truth may change, but those facts are still the same. But if that isn't the line, what is?
Additionally, if truth is relative, then statements such as, "Murder is wrong" are not necessarily true for all people. Just to point out the obvious example here, how can we blame Hitler for his genocide of the Jews when he thought that he was advancing society? That was the truth "for him." It was of course, not truth at all, but if there was no absolute truth, could we condemn him for these heinous actions? The logical conclusion of relativism is that we can't punish murderers and other criminals if they believe their actions to be right. For that reason, I must accept that there is an absolute knowable truth.
Do you think that I am just sprouting extreme examples for the purpose of argument? That's a fair concern. In answer, I urge you to read some works of relativists in history, such as Friedrich Nietzsche, Thrasymachus, and Protagoras, all of whom view ethics and morals as a lie perpetrated by society. Nietzsche would even go as far as saying that our criminals are "supermen" because they have stood up to society's "herd morality." A world without morals is very irrational and absurd (indeed Nietzsche admits this himself). Thus, in order to determine which belief we would like to assume to be true, it makes much more sense to assume there is absolute truth.