According to the Oxford dictionary the word "dual" means being twofold. In philosophy there is the theory of "dualism" that argues that any domain of reality is always underpinned by two independent, opposing principles, for example, mind and matter, form and content, idealism and materialism, etc. In many of the theologies and religions of the world we also find the pervasive idea that the forces of good and evil are equally balanced in the universe. Another common idea is that of the dual nature of human beings, existing both in body and spirit. In the Christian doctrine there is also the belief in the dual personality of Christ (human and divine).