Dualism is the position that both mind and body exist. They are separate kinds of substance. In Descartes view they interact. The mind moves the body. If they are separate substances then they ought to exist independently. we should be able to observe a mind and a body separately. Secondly, if they are separate the mind should be able to occupy another body.

What we observe though is not two entities. A concrete entity is a one that has spatial temporal location, brings about effects, perceptible by the senses. If the mind was a concrete entity it should have these characteristics. It does not. One thing about objects is that they are impenetrable. So another question is how is mind and body able to occupy the same space?

So not only are we not observing two entities, we are not seeing exception to rules about impenetrability.

Perhaps mind is about a thing. Perhaps mind is like walking, a property of a thing.

We may say this mind or that mind. We may even talk about mind in plural form – minds. But is this not reification? Should we not be talking about this thinking person or that thinking person?

It is far easier to reify something, to turn actions, qualities, relations into objects. Language and minds allow this. Reality and the way we think about reality does not match. And the way think about the mind is one area this is most evident.