In Metaphysics, 'dualism' designates an ontological position that asserts there is more than one kind of stuff in the Universe. There are two types of dualist theories:

  1. Substance Dualism

  2. Property Dualism

Substance Dualism is the most common form of dualism and maintains there are two distinct and properly basic substances in the Universe: matter and mind. Both substances are elemental, or properly basic, substances (or stuffs) so that neither can be reduced to the other. According to this theory humans are minds (or souls) inside bodies.

Property Dualism holds that minds or mental events are properties which emerge from a particular organization of matter.