W. T. Stace, A critical history of Greek philosophy
“ If, for example, we say that all the good in the universe arises from one source which is good, and that all the evil arises from another source which is evil, and that these sources of good and evil cannot be subordinated one to the other, and that one does not arise out of the other, but both are co-ordinate and equally primeval and independent, that position would be a dualism. ”
