Rta literally means the "course of things." At first, the early Hindus were notably confused as to the inscrutable order of nature, how the heavenly bodies, the rushing winds and flowing waters, the consistent cycling of the seasons, were regulated. Thenceforth sprang rta, whose all-purpose role it was to signify this order, the path that was always followed. Through all the metamorphoses and permutations of nature, of life in general, there was one unchangeable fact: rta.
In the Vedas, which span back to 2000 BCE (and further in oral tradition), Rta lays the philosophical foundation for dharma seen in the Hindu context. In current usage, the use of the word rta is eschewed for the more developed and now standard dharma.
Soon it transcended its passive role as a mere signifier and took on a greater one, that of an active imposition of order. Not only the natural principles, but the gods and goddesses themselves, were obliged to abide by rta. Rta became the father, the law of justice and righteousness, unyielding but eminently fair. It grew, as Radhakrishnan states, from "physical" to "divine" in its purvey.
The world's seeming mess of altercating fortune, the caprice of the divinities, was now intelligible. Indeed, there was a single, unchanging harmony working 'behind the scenes.' A right path existed, ready to be taken by the righteous ones. Rta signifies the way life ought to be, shifting from physical to divine, from natural to moral order. Rta was morality, the equitable law of the universe. The conception of this all-transcending, supramental force that is, practically, the same concept as later understandings of dharma, is captured in this early Vedic prayer, preempting the liturgical strains of classical Hindu mantras involving dharma:
"O Indra, lead us on the path of Rta, on the right path over all evils."
--(Rig Veda Book X, Chapter CXXXIII, Verse 6)
Thus we see the logical progression of an early 'course of things' into an all-encompassing moral order, a path and way of righteousness, an all-encompassing harmony of the universe, in the Vedic idea of Rta.
