The most incomprehensible thing about the universe is that it is comprehensible. -Albert EinsteinI'll start with the reminder that philosophy is neither my vocation, hobby (avocation), or education. But my college degree did include snazzy liberal arts classes. (The only course I disdained was art, in which I received low grades for my art criticism. My excuse could be either the indeterminate basis for evaluation, the capricious professor, or the unmitigated subjectivity of the "correct" answer. Yeah, I'm bitter.)
My definition of philosophical Truth is straightforward if ridiculously unoriginal: Truth does not exist. In more precise language, truth isn't transcendental. It's a common noun, not a proper noun (notice the capitalization difference?). It's never found alone because it's the measure of the correspondence between specific thoughts and reality. Where there's no thought, there's no truth. Where there's no reality, there's no truth.
This definition of Truth has the advantage of matching the way that all people learn what truth is. Truth is not lying. A lie is detected by comparing the statement to ascertained reality. Even the fictional truth of a fictional statement uttered by a fictional character can't be judged without reference to the fictional world it's from. A statement that cannot be disproved is neither lie nor truth. When people have wondered out loud to me whether reality is "really" the Dream of an unknown Dreamer, my reply has amounted to "So what?"
Another reply I could make to the same conjecture is "For being a Dream, reality is much more ordered than what I experienced when I was sleeping last night". And this reply also expresses something about the discovered nature of (common, not transcendental) truth. Reality is experienced as orderly. It's also unfathomably complicated from moment to moment, but orderly nonetheless. In fact, as creatures who have developed to productively interact with our environment, we're "hard-wired" to quickly generalize and then apply patterns, a strategy that would fail if reality had none. Thus, we repeatedly confirm the applicability of patterns to reality so often that it's strange to mention it. Since the patterns correspond to reality, by definition the patterns have truth. Moreover the pattern-making process must have truth for it to produce so many truthful patterns. But what is the usual philosophical term for the patterns and the pattern-making process? Reason. Reason has truth because it produces thoughts that correspond to reality, but reason couldn't produce those true thoughts from other true thoughts unless it operated in a way that corresponded to reality. For instance, predicting an object's future location based on its current trajectory works because objects don't change trajectory without cause. Reason works because it has truth. When reason stops working it's no longer (perfectly) corresponding to reality, and by the definition no longer has (the same amount of) truth.
However, since transcendent truth is nonexistent, transcendently-truthful reason is nonexistent, too. Similar to truth, reason is a lower-cased common noun. Put simply, reason doesn't always yield truth. Reality doesn't guarantee a confirmation of reason, seeing as how it doesn't guarantee a confirmation of any proposition or statement or thought. Reality overwhelms the capability of every example of reason sooner or later. Reality is not perfectly predictable. It's not computable in its totality, not even by an impossible all-knowing demon. Reality is endlessly astounding.
Nevertheless, I'll attempt to reason out anticipated questions in a second part.