Dualism in cosmology or dualistic cosmology is the moral or spiritual belief that two fundamental concepts exist, which often oppose each other. It is an umbrella term that covers a diversity of views from various religions, including both traditional religions and scriptural religions.

Twins appear in the mythologies of many cultures around the world. In some cultures they are seen as ominous, and in others they are seen as auspicious. Twins in mythology are often cast as two halves of the same whole, sharing a bond deeper than that of ordinary siblings, or seen as fierce rivals. They can be seen as representations of a dualistic worldview. They can represent another aspect of the self, a doppelgänger, or a shadow.