What is metaphysical dualism?
Not in Greece. Seventeenth century Europe. Dualism is the practice of identifying a perception of reality by strong, logical argument (“I think, therefore I am”), and also identifying reality by a reference to God, thus: “First, I know that everything which I clearly and distinctly understand is capable of being created by God so as to correspond exactly with my understanding. Hence, the fact that I can clearly and distinctly understand one thing apart from another is enough to make me certain that the two things are distinct, since they are capable of being separated, at least by God… Thus, simply by knowing that I exist and seeing at the same time that absolutely nothing else belongs to my nature or essence except that I am a thinking thing. It is true that I may have (or, to anticipate, that I certainly have) a body that is very closely joined to me. But nevertheless, on the one hand I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing;
Metaphysical dualism is typically considered to be the notion that there are two types or substances. A substance is that which underlies the changing world and makes it retain enough identity to change. When you see a picture of yourself at five, you don’t say what the hell is that! but oh that is me. However, you are different now then you were then, so what is it that makes you the same person? This is what is meant by substance. Now to your question, dualism is the belief that there are two types of underlying substances to the world. In modern philosophy the most classic proponent of this view would be Descartes (there is mind which is a different substance than body). The clearest example of this is in Ancient Greece is Plato. The Forms are non-spatial and non-temporal, but everything we encounter down here on earth is spatial and temporal. Objections could be raised that the substance of the world is the Forms and the things of the world are merely distorted images of the Forms.
