Dualism
The view that mind and matter are fundamentally different kinds of thing, so mental states are not simply physical states of the body.
In practice
The intuition that a complete brain scan could tell you everything about what someone is doing and still not tell you what they are experiencing is the dualist intuition, whatever you conclude from it.
The common mistake
Assuming dualism means believing in souls. Property dualism posits no additional substance and is defended by philosophers with no religious commitment at all.
Dualism holds that the mental and the physical are distinct in kind. It is the position most people arrive at without instruction, and the one most philosophers of mind reject.
Substance dualism
Descartes gave the classic version in 1641. Mind is thinking and unextended; body is extended and unthinking. They are two kinds of substance, which explains neatly why mental states seem so unlike physical ones.
The objection arrived immediately, from Princess Elisabeth of Bohemia: if the mind has no extension and no physical properties, how does it move anything? Causation between two substances sharing no properties has never received a workable account, and the difficulty is generally treated as decisive against this form. See the mind-body problem.
Property dualism
The version with living defenders. There is one kind of substance, the physical, but it has two kinds of property — physical ones and irreducibly mental ones. Conscious states are properties of brains and are not reducible to their physical properties.
This avoids asking how two substances interact while keeping what dualists want to preserve: that qualia are not captured by a functional story. Its own difficulty is epiphenomenalism — if mental properties do no causal work the physical ones are not already doing, it is hard to see why they exist or how we could know about them.
The case against
Causal closure. Physics appears complete: every physical event has a sufficient physical cause. If so, there is no work left for a non-physical mind, and dualism implies either that physics is incomplete or that mind does nothing.
Dependence. Damage the brain and the mind changes in specific, predictable ways. That is what you would expect if mental states are brain states, and it takes explaining otherwise.
Why it persists
Because the alternative has not closed the explanatory gap. Whatever the difficulties, dualism takes seriously something the competing views tend to set aside — that there is something it is like to be a person, and no account of mechanism has yet explained why. See materialism and idealism.
Concept web
Open the full webQuestions
What is dualism in philosophy of mind?
The view that mind and matter are fundamentally different kinds of thing. Substance dualism treats them as two kinds of substance; property dualism treats mental properties as irreducible properties of physical things.
What is the main objection to dualism?
Causal closure. Physics appears to provide a sufficient physical cause for every physical event, which leaves a non-physical mind either doing nothing or requiring that physics be incomplete.
What is property dualism?
The view that there is only physical substance but that it has irreducibly mental properties. It avoids the interaction problem and faces the difficulty of explaining what causal work those properties do.