Truth is traditionally defined as that which cannot not be; it is necessary by its nature; it also has to be absolute. What is relative is dependent, and hence not marked by necessity but rather by accident.
Truth cannot belong to the sphere of Being and existence; it is not something that can be said to be or not to be, to exist or not to exist. Something that exists can also be conceived of as not existing. The non-Being of something that is in Being is a logical appendix to its Being. But truth is that which whose non-Being cannot be conceived of. Thus, it cannot belong to the sphere of Being or among beings. Truth has to be beyond Being if it is truth at all. Something that is in Being does not qualify as truth.
From necessity and absoluteness it follows that truth has to be one and unique; if there are two truths that are not identical, then the necessity of one excludes the necessity of the other by definition unless otherwise they are identical. Therefore, if we have two truths, either they are identical or else none of them is truth.
Therefore, truth is that which is unique, necessary, absolute, and beyond Being. Metaphysically speaking, truth is One, Unique, Absolute, Infinite, and by necessity both immanent and transcendent at once. However, anything that can be put into a proposition belongs to the sphere of being. Proposition is an assertion, a predication. The negation of that which is predicated is always conceivable; thus, truth cannot be something to be predicated on something. Proposition can only house facts; fact is by definition relative and contingent.
Yada, yada, yada… Truth is something that can only be experienced. It is something to be seen rather than asserted. It is in the nature of truth, logically and ontologically and metaphysically, that it cannot be put into proposition; it has to be experienced. But it can only be experienced transcendentally because all natural experiences pertain to contingent facts. World is a body of facts, facts being essentially relative and contingent; hence, no natural experience such as seeing or hearing or believing can grasp truth.
The experience of truth has to be absolute and self-evident. The self-evidence of truth lies in the truth itself and not provided from outside it by way of argumentation or logical demonstration or experiment. Only facts are shown in experiments. This means that you cannot at once experience the truth and also entertain even the slightest doubt whether it is truth or not: Truth is that which cannot not be. This is the best guide for the aspirant. As long as one can ask himself whether this is it or not, it is sure that it is not it; when you see the truth you will know, and you will know with absolute certainty such that it is not possible at all to doubt it. This arises from the essence of truth.
The face of truth is its own proof.
It is said that “Truth is infinitely close to us while we are infinitely far from truth.”
Of course, none of the above proves that there is such a thing as truth; but if there is it has to have the above essential characteristics by definition.
To go after the proof for truth is pointless. Since truth is not a thing to be put into proposition or predicated, it is not something to be proved. And there are things that exist but cannot be proved: Color exists, though it exists in experience; it is something experienced. But it is impossible to prove to a blind man the existence of color and what it is like.
Things that exist in experience are things that transcend proof; proof does not apply to them, for their truth is established in and through experience and not through logical or rational demonstration. Thus, the lack of proof does not prove anything. Those whose first attack to metaphysical truth is “prove it” really have not understood the first thing about logic. The best answer to them is to ask them to “prove that proof is the only method of demonstration.” The example of color and the blind man is the counterexample.
Truth, too, since it is something experienced, cannot be proven or disproven; it is either seen or not seen; and he/she who has seen it needs no proof whatsoever.