Property dualism

Property dualism

. In other words, it is the view that non-physical, mental properties (such as beliefs, desires and emotions) adhere in some physical substances (namely brains).

Substance dualism, on the other hand, is the view that there exist two kinds of substance: physical and non-physical (the mind), and subsequently also two kinds of properties which adhere in those respective substances. The term property dualism however generally refers only to those positions which can oscillate between the existence of physical substances. So, with one hand, you can wave hello, or wave goodbye.

Non-reductive Physicalism

Non-reductive physicalism is the predominant contemporary form of property dualism according to which mental properties are in some sense identical with neurobiological properties, but are not reducible to them.

Reductive physicalists, by contrast, maintain that mental properties are entirely reducible to neurobiological properties, in much the same way that water is reducible to H2O and light is reducible to electro-magnetic radiation. Mental properties, it will turn out, are nothing over and above the various physical states of the brain.

Non-reductive physicalists deny that mental properties are reducible to physical properties in this manner. They maintain that mental properties "are" something over and above their neurobiological counterparts, comprising their own ontological class of property.

Token Identity

When talking about mental properties being identical to physical properties, it is important to note the difference between type identity and token identity. To use the philosophical jargon, type identity is identity that holds between universals, while token identity holds between particulars. Universals are concepts we use to describe a class of objects; for example the term "computer" picks out a number of objects in the world, namely those that meet our definition of what a computer is. The machine you are sitting in front of however is a particular - or token - a single specific object. In the sentence "again and again and again and again" it could be said that there are two words, or it could be said that there are seven. To say there are two is to pick out two types, and to say that there are seven is to pick out seven tokens.

So when we say that the mental property of pain is type-identical with a particular neurobiological property (the common example is C-fibre stimulation) we mean that "all" instances of pain are instances of C-fibre stimulation; the universals "pain" and "C-fibre stimulation" pick out one and the same thing in the world. However to say that pain is token-identical with C-fibre stimulation is to say something quite different, namely that this instance of pain is identical with this instance of C-fibre stimulation. It is possible under token identity that a different instance of pain is not identical with C-fibre stimulation, but something else entirely, or nothing else at all.

Reductive physicalism requires type identity between mental and neurobiological properties. Non-reductive physicalism, however, tends to adopt only token-identity between mental and neurobiological properties. This has the important consequence that different instances of mental types - e.g., pain - can be identical with completely different neurobiological properties on different occasions or within different species.


Non-reductive physicalists most commonly describe the token identity relationship between instances of mental and physical properties as one of supervenience.

The concept of supervenience is borrowed from moral (and later aesthetic) philosophy. where it is thought that moral properties, such as goodness, are supervenient on naturalistic properties, such as kindness, benevolence and courage. The supervenient, or higher-level property is in this sense dependent upon the ‘base’, or lower-level property (or properties); any change in the higher level properties requires a change in the lower-level properties.

Applied to the philosophy of mind, mental properties can be said to similarly supervene on lower level, neurobiological properties. So while mental properties are dependent for their existence on neurobiological properties, they remain ontologically intact; they are something "over and above" the processes of the brain.

"--For arguments for and against non-reductive physicalism, see the physicalism page--"


Epiphenomenalism is a version of non-reductive physicalism which holds that mental properties are the byproducts (or epiphenomena) of the states of a closed physical system. 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 favour amongst scientific behaviourists over the next few decades, until behaviourism itself fell to the cognitive revolution in the 1960s. Recently, epiphenomenalism has gained popularity with those struggling to reconcile non-reductive physicalism and mental causation.

"-- See the epiphenomenalism page for further discussion and arguments for and against the position --"

Anomalous Monism

Most contemporary non-reductive physicalists subscribe to a position called anomalous monism (or something very similar to it). Unlike epiphenomenalism, which renders mental properties causally redundant, anomalous monists want to hold onto the idea that mental properties can make a causal difference to the world.

The position was originally put forward by Donald Davidson in his 1970 paper "Mental Events", and holds that in addition to this principle of causal interaction between the mental and the physical, two other principles can also be granted. One is the "nomological character of causality" - the idea that when two events are in causal relation to one another, there must be a strict law connecting them (i.e. the occurrence of the cause must by law guarantee the occurrence of the effect). Davidson's third principle is the "anomalism of the mental", which states that the kind of strict deterministic law described above cannot apply to the mental events, which can be neither predicted nor explained in a decisively law-like manner. The mental is rather governed by ‘guidelines’ of normativity. These three principles, Davidson claims, are incompatible. We can accept any two but not the third, lest we be led into contradiction.

There is only one way to resolve this Mexican stand-off, according to Davidson, and that is to stake an identity claim between mental and physical tokens based on the notion of supervenience (see below). If mental events are identical to physical events, then they can enter into strict law-governed causal relationships, upholding the first and second principles. But since mental properties are supervenient on, and so not reducible to, physical properties, they can retain their anomological status, preserving the third principle.

"--See the anomalous monism page for further discussion, and arguments for and against the position--"

Emergent Materialism

The antithesis of reductionism, emergentism is the idea that increasingly complex structures in the world give rise to the "emergence" of new properties that are something over and above (i.e. cannot be reduced to) their more basic constituents. The concept of emergence dates back to the late 19th century. John Stuart Mill notably argued for an emergentist conception of science in his 1843 "System of Logic"

Applied to the mind/body relation, emergent materialism is another way of describing the non-reductive physcialist conception of the mind that asserts that when matter is organised in the appropriate way (i.e., organised in the way that living human bodies are organised), mental properties emerge.

Arguments for

The Knowledge argument

Perhaps the most famous argument in favour of a property dualist ontology is
Frank Jackson's thought experiment involving Mary the super scientist; sometimes called the knowledge argument. Let us suppose, Jackson suggests, that a particularly brilliant super-scientist named Mary has been locked away in a completely black-and-white room her entire life. Over the years in her colour-deprived world she has studied (via black-and-white books and television) the sciences of neurophysiology, vision and electromagnetics to their fullest extent; eventually Mary comes to know all the physical facts there are to know about experiencing colour. When Mary is released from her room and experiences colour for the first time, does she learn something new? If we answer "yes" (as Jackson suggests we do) to this question, then we have supposedly committed ourselves to property dualism. For if Mary has exhausted all the physical facts about experiencing colour prior to her release, then her subsequent encounter with some new property of colour upon experiencing its quale reveals that there must be something about the experience of colour which is not captured by the physicalist picture. Some properties, it would seem, must be non-physical.

Arguments against

The causal inefficacy of mental properties


* Davidson, D. (1970) "Mental Events", in Actions and Events, Oxford: Clarendon Press, 1980
* Huxley, Thomas. (1874) "On the Hypothesis that Animals are Automata, and its History", The Fortnightly Review, n.s. 16, pp. 555-580. Reprinted in Method and Results: Essays by Thomas H. Huxley (New York: D. Appleton and Company, 1898)
* Jackson, F. (1982) "Epiphenomenal Qualia", The Philosophical Quarterly 32: 127-136.
* Kim, Jeagown. (1993) "Supervenience and Mind", Cambridge: Cambridge University Press.
* MacLaughlin, B. (1992) "The Rise and Fall of British Emergentism", in Beckerman, et al. (eds), Emergence or Reduction?, Berlin: De Gruyter.
* Mill, John Stuart (1843). "System of Logic". London: Longmans, Green, Reader, and Dyer. [8th ed., 1872] .

See also

* Biological naturalism
* Physicalism
* Anomalous Monism
* Dualism (philosophy of mind)
* Emergence
* Materialism
* Mind-body problem
* Monism

External links

* [ M. D. Robertson: Dualism vs. Materialism: A Response to Paul Churchland]
* [ Stanford Encyclopedia of Philosophy: Dualism]
* [ Stanford Encyclopedia of Philosophy: Epiphenomenalism]
* [ Stanford Encyclopedia of Philosophy: Physicalism]

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