A leftist friend writes that he is not a relativist, but he does hold that truth keeps evolving: “Every truth we assert today will someday be supplanted by a more comprehensive truth.”
But this is not possible. A truth that becomes untrue with time or greater knowledge was never a truth. It was always an error.
If everything we knew before, and everything we know now, is in error, we know nothing about anything. And, logically, we never will. There will always be a more comprehensive truth to come along, or, even if not, we still cannot know there will not be.
This leaves truth as, if not relative, worse than relative, irrelevant. Because of the insurmountable epistemological problem, you might just as well pick your beliefs at random. Just as likely to be true.
No: for truth to have any meaning, we must indeed always perceive some truths, which we can contrast with opinions, beliefs, and errors; and we must always have been able to perceive some truths. Two and two equal four. A thing cannot be true and false simultaneously. There are no square circles.
Further, if one posits the existence of a God—that is, if one does not accept that the existence of God is itself a self-evident truth--it follows that we are and were always able to perceive at least all the essential truths at all times. A benevolent Deity would necessarily have made it so.
Accordingly, religious truth does not evolve and change. It is only clarified over time.
Too many are misled by the example of science, and the fact that scientific understanding does indeed evolve and change. This is an important criticism of science—that it never arrives at truth, only at useful models of truth. But one must not reify this to philosophy or to human thought in general.