There is but one cosmos. There can be but one fundamental truth about that cosmos. -- G. de Purucker
In pondering the question "What is truth?" we can arrive at only a broad conception of what it is. Truth with a capital T may be defined as Reality with a capital R. The Oxford English Dictionary defines truth as "agreement with reality"; it must agree, for the two are essentially one. So, what is reality? The OED definition is "that which underlies and is the truth of appearances and phenomena."
Perhaps there is a great or absolute Truth which we can never know. We do know certain things, however, so there must be relative truths -- truths which we can perceive even in this world of appearances and illusion (maya). A maxim in the Persian Javidan Khirad reads: "Truth is of two kinds -- one manifest and self-evident; the other demanding incessantly new demonstrations and proofs." The latter will in time become universally obvious, and then the two will once more be one.
James A. Long described truth as the horizon that "ever eludes us but is always before us":
When we want to know what is beyond the horizon, we travel the road that leads toward it. But when we arrive, the horizon has moved on; and it will always move on. just so with truth: we shall never reach the "last horizon," because there will always be another and another. -- Expanding Horizons, p. 64
Truth has at times been equated with dogma -- a word with a long history. Originally from the Greek dokein, to seem, dogma has come to mean a doctrine authoritatively imposed or established. It is what in mathematics would be considered a "closed set." This is obviously counter to an "open set" in which one could add new, or delete invalid, information as circumstances require. Even in its technical teachings theosophy is wholly nondogmatic and its students subscribe to the statement made by Jesus: "If any man hear my words, and believe not, I judge him not" (John 12:47). Each one of us must find the key of nature within and test the knowledge of the world for ourselves, as the sages do with esoteric truths. Every human being has within himself the touchstone by which to test reality.
What then is proof and why is it so important? Proof may be defined as conclusive evidence. We need, however, to be careful of the validity of the evidence for it can confound and even destroy earthly lives. Our inner touchstone can become our true guide in life; it should not be able to be swayed as our intellect can be when working alone, divorced from that inner guidance. There is an infallible test, according to G. de Purucker, by which to judge any teaching -- this test is universality. If a teaching is true in all contexts, under all conditions, in all aspects of nature, to all major philosophic and religious insights, then it must be true in principle. This means agreement at the heart of things and on all levels. Verse 54 of the Dhammapada states:
The fragrance of flowers does not travel against the wind, be it that of sandalwood, of tagara, or jasmine. But the fragrance of the virtuous man travels even against the wind. The virtuous man pervades all directions with his purity. -- Canto 4, trans. H. Kaviratna
Nature, universal nature, operates by laws regardless of any teaching being true or false; yet it is the true conception thereof, the wonderfully beautiful one, which we will see forever. To see the beauty of the universe is to catch a glimpse of truth. As John Keats wrote in his "Ode on a Grecian Urn":
When old age shall this generation waste,
Thou shalt remain, in midst of other woe
Than ours, a friend to man, to whom thou say'st,
"Beauty is truth, truth beauty," -- that is all
Ye know on earth, and all ye need to know.