The Dûnyain are a severe monastic sect that has repudiated history and animal appetite in the name of finding enlightenment through the control of all desire and all circumstance. Their name means "Truth".
Though the origins of the Dûnyain are obscure (many think them the descendants of the ecstatic sects that arose across the Ancient North in the days preceding the Apocalypse), their belief system is utterly unique, leading some to conclude their original inspiration had to be philosophical rather than religious in any traditional sense.
Much of Dûnyain belief follows from their interpretation of what they consider their founding principles. The Emperical Priority Principle (sometimes referred to as the Principle of Before and After) asserts that within the circle of the world, what comes before determines what comes after without exception. The Rational Priority Principle asserts that Logos, or Reason, lies outside the circle of the world (though only in a formal and not an ontological sense). The Epistemological Principle asserts that knowing what comes before (via the Logos) yields "control" of what comes after.
Given the Priority Principle, it follows that thought, which falls within the circuit of the before and after, is also determined by what comes before. The Dûnyain therefore believe the will to be illusory, an artifact of the soul's inability to perceive what comes before it. The soul, in the Dûnyain world view, is part of the world, and therefore as much driven by prior events as anything else. (This stands in stark contrast to the dominant stream of Three Seas and Ancient North thought, where the soul is taken to be, in Ajencis's words, "that which precedes everything.")
In other words, Men do not possess "self-moving souls". Far from a given, such a soul is an accomplishment for the Dûnyain. All souls, they claim, possess conatus, the natural striving to be self-moving, to escape the circle of before and after. They naturally seek to know the world about them and so climb out of the circle. But a host of factors make outright escape impossible. The soul men are born with is too obtuse and clouded by animal passions to be anything other than a slave of what comes before. The whole point of the Dûnyain ethos is to overcome these limitations and so become a self-moving soul -- to attain what they call the Absolute, or the Unconditioned Soul.
But unlike those exotic Nilnameshi sects devoted to various other forms of "enlightenment", the Dûnyain are not so naive as to think this can be attained within the course of a single lifetime. They think of this, rather, as a multi-generational process. Quite early on they recognized that the instrument itself, the soul, was flawed, so they instituted a program of selective breeding for intellect and dispassion. In a sense the entire sect became a kind of experiment, isolated from the world to maintain control, with each prior generation training the next to the limit of their capabilities, the idea being that over the millennia they would produce souls that could climb further and further from the circle of before and after. The hope was that eventually they would produce a soul utterly transparent to Logos, a soul capable of apprehending all the darknesses that come before.
After two thousand years of isolation and selective breeding, Dûnyain genetics have changed to the point where they have difficulty interbreeding with normal humans. The offspring of such couplings have a high risk of birth defects. The ones that survive tend to have intellects superior to normal humans but inferior to pure Dûnyain.