Human nature, as a dynamic concept, thus spreads itself along a course that reason and morality may plot. Central in the scientific view is the contention that human nature is malleable and that it is subject to cultural alteration. Revolutionary thought, which carries in it the idea of a malleable and progressive human nature, is mixed with deterministic ideas that suggest the impossibility of changing men at least until the new society is formed. Most revolutionary thought assumes that human nature is good, or, at least, that it is trustworthy under the influence of knowledge. The conservative has sought to limit reform and Utopian revolution by insisting that human nature is a mixture of rational and irrational behavior, and that man is a blending of cooperation and recalcitrance. The iron curtain across Central Europe was drawn by power politics and not by political theory, though ideology has played its part in justifying it.