While the tetrad gods are the only true gods in Tariksan, there are several ways to have a functioning religious system that doesn't directly refer to them. The simplest is a god of a forgotten Tetrad, where any links to other gods are long forgotten. But there exists worship of saints, pure concepts (and fictional gods that symbolise these concepts), physical embodiments of cosmic ideas, otherplanar beings, and the many faces of Discanil, the god of lies. And there are religions like those today, based almost entirely on pure belief.