The following is a slightly expanded version of my comments under the thread “The Empire of Lies”, an essay from John C. Wright (February 13, 2016).
“Either there is truth or there is not.”
After this opening line, Mr. Wright proceeds to demonstrate that the statement “there is no truth” is impossible and self-destroying, an absurdity even if only for the sake of argument. Such an argument is sustained solely for expediency, for moral reasons, in order to pass vice for virtue, virtue for vice, and evildoing for good works. In short, nihilism.
The origin of such extreme moral outlook is sin unacknowledged, unrepented, and conscience stifled accordingly. As Jacques Maritain explained, when we sin, the will (or the “reason of the heart” as Blaise Pascal would put it) listens to emotions and sentiments and averts its inner eye from the sound principles of the practical intellect, that is, the truth as seen by the conscience. By blurring objective truth about the objective good, the will is generally able to trick a poorly formed conscience into taking an evil for a good, or a lesser good for a greater good, or evil means as expedient to attain some good.
But the guilt remains. To evade the guilt efficiently, there is no other way than to attack the principles, the axioms themselves (identity, reason for being, finality, causality, etc.), and ultimately the transcendentals above the principles: no objective beauty, goodness or truth, thus no moral obligation.
Now, what is truth? The shortest and simplest definition is: Truth is the conformity of the mind to things. An honest search for truth makes licit almost any question. For example, the question “Either there is a God (or gods), or there is not” implies that the human mind might be able to discover the truth, or accept the revelation of truth.
If there are things, there is a God, because nothing contingent can exist if there is no necessary being which is the first cause and reason for being of everything else. Hence the same reasoning applies to truth: if there is something, there is truth in the same measure that things do exist and are good and beautiful, and at least partly knowable.