Latin: duo, two

1) The system accounting for the universe as caused by two conflicting principles, good and evil.

2) The existence in the world of two kinds of being or substance, matter and mind, produced by one and the same cause. Between these two beings there is a substantial union, so that they act together as one. Through the matter of the body, the senses, comes to the soul the knowledge of external objects. It was Descartes‘ failure to grasp the fact of this union which led to the many false philosophical theories of our day assuming that there is an impassable breach between mind and matter and, as a consequence, that knowledge is subjective with no element of external reality.