Property dualism



Property dualism describes a category of positions in the philosophy of mind which hold that, although the world is composed of just one kind of substance—the physical kind—there exist two distinct kinds of properties: physical properties and mental properties. In other words, it is the view that at least some non-physical, mental properties (such as thoughts, imagination and memories) exist in, or naturally supervene upon, certain physical substances (namely brains).

Substance dualism, on the other hand, is the view that there exist in the universe two fundamentally different kinds of substance: physical (matter) and non-physical (mind or consciousness), and subsequently also two kinds of properties which inhere in those respective substances. Substance dualism is thus more susceptible to the mind–body problem. Both substance and property dualism are opposed to reductive physicalism.

Epiphenomenalism
Epiphenomenalism is a doctrine about mental-physical causal relations which holds that one or more mental states and their properties are the by-products (or epiphenomena) of the states of a closed physical system, and are not causally reducible to physical states (do not have any influence on physical states). According to this view, mental properties are as such real constituents of the world, but they are causally impotent; while physical causes give rise to mental properties like sensations, volition, ideas, etc., such mental phenomena themselves cause nothing further - they are causal dead ends. The position is credited to English biologist Thomas Huxley (Huxley 1874), who analogised mental properties to the whistle on a steam locomotive. The position found a level of favor amongst some scientific behaviorists over the next few decades, which then dove in response to the cognitive revolution in the 1960s.

Epiphenomenal qualia
In the paper "Epiphenomenal Qualia" and later "What Mary Didn't Know" Frank Jackson made the so-called knowledge argument against physicalism. The thought experiment was originally proposed by Jackson as follows:

Jackson continued:

"It seems just obvious that she will learn something about the world and our visual experience of it. But then it is inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo, there is more to have than that, and Physicalism is false."

Panpsychist property dualism
Panpsychism is the view that all matter has a mental aspect, or, alternatively, all objects have a unified center of experience or point of view. Superficially, it seems to be a form of property dualism, since it regards everything as having both mental and physical properties. However, some panpsychists say that mechanical behaviour is derived from the primitive mentality of atoms and molecules &mdash; as are sophisticated mentality and organic behaviour, the difference being attributed to the presence or absence of complex structure in a compound object. So long as the reduction of non-mental properties to mental ones is in place, panpsychism is not strictly a form of property dualism; otherwise it is.

David Chalmers has expressed sympathy for panpsychism (or at least for a modified variant, called panprotopsychism) as a possible resolution to the hard problem of consciousness, though he regards the combination problem as an important obstacle for the theory. Other philosophers who have taken interest in the view include Thomas Nagel, Galen Strawson, Timothy Sprigge, William Seager, and Philip Goff.

Subjective idealism
Subjective idealism, proposed in the eighteenth century by George Berkeley, is an ontic doctrine that directly opposes materialism or physicalism. It does not admit ontic property dualism, but does admit epistemic property dualism. It is rarely advocated by philosophers nowadays.

Saul Kripke
Kripke has a well-known argument for some kind of property dualism. Using the concept of rigid designators, he states that if dualism is logically possible, then it is the case.