Mind–body dualism
In the philosophy of mind, mind–body dualism denotes either that mental phenomena are non-physical, or that the mind and body are distinct and separable. Thus, it encompasses a set of views about the relationship between mind and matter, as well as between subject and object, and is contrasted with other positions, such as physicalism and enactivism, in the mind–body problem.
Aristotle shared Plato's view of multiple souls and further elaborated a hierarchical arrangement, corresponding to the distinctive functions of plants, animals, and humans: a nutritive soul of growth and metabolism that all three share; a perceptive soul of pain, pleasure, and desire that only humans and other animals share; and the faculty of reason that is unique to humans only. In this view, a soul is the hylomorphic form of a viable organism, wherein each level of the hierarchy formally supervenes upon the substance of the preceding level. For Aristotle, the first two souls, based on the body, perish when the living organism dies, whereas there remains an immortal and perpetual intellective part of mind. For Plato, however, the soul was not dependent on the physical body; he believed in metempsychosis, the migration of the soul to a new physical body. It has been considered a form of reductionism by some philosophers, since it enables the tendency to ignore very big groups of variables by its assumed association with the mind or the body, and not for its real value when it comes to explaining or predicting a studied phenomenon.
Dualism is closely associated with the thought of René Descartes, who holds that the mind is a nonphysical—and therefore, non-spatial—substance. Descartes clearly identified the mind with consciousness and self-awareness and distinguished this from the physical brain as the seat of intelligence. Hence, he was the first documented Western philosopher to formulate the mind–body problem in the form in which it exists today. However, the theory of substance dualism has many advocates in contemporary philosophy such as Richard Swinburne, William Hasker, J. P. Moreland, E. J. Low, Charles Taliaferro, Seyyed Jaaber Mousavirad, and John Foster.
Dualism is contrasted with various kinds of monism. Substance dualism is contrasted with all forms of materialism, but property dualism may be considered a form of non-reductive physicalism.
Types
dualism makes dual commitments about the nature of existence as it relates to mind and matter, and can be divided into three different types:- Substance dualism asserts that mind and matter are fundamentally distinct kinds of foundations.
- Property dualism suggests that the ontological distinction lies in the differences between properties of mind and matter.
- Predicate dualism claims the irreducibility of mental predicates to physical predicates.
Substance or Cartesian dualism
Cartesian dualism, most famously defended by René Descartes, argues that there are two kinds of substances: mental and physical. Descartes states that the mental can exist outside of the body, and the body cannot think. Substance dualism is important historically for having given rise to much thought regarding the famous mind–body problem. It is compatible with theologies which claim that immortal souls occupy an independent realm of existence distinct from that of the physical world. Cartesians tend to equate the soul to the mind.
The Copernican Revolution and the scientific discoveries of the 17th century reinforced the belief that the scientific method was the unique way of knowledge. Bodies were seen as biological organisms to be studied in their constituent parts by means of anatomy, physiology, biochemistry and physics. Mind–body dualism remained the biomedical paradigm and model for the following three centuries.
Emergent dualism
Emergent dualism is a type of substance dualism that has been defended by William Hasker and Dean Zimmerman. Emergent dualism asserts that mental substances come into existence when physical systems such as the brain reach a sufficient level of complexity. Hasker defines emergent dualism as:Hasker has argued that emergent dualism is consistent with neuroscientific discoveries showing the dependence of mind on brain. He likens the individual mind to a magnetic field in its qualitative difference from the physical properties that generate it and also in its ability to act on the brain that generates it. Consciousness is said to arise when the brain reaches a certain threshold level of organizational complexity and when properly organized gives rise to the soul.
Thomistic dualism
Thomistic dualism is a type of dualism derived from the views of Thomas Aquinas. Edward Feser has written that:Thomistic substance dualism has been defended by J. P. Moreland and Scott B. Rae. Thomistic substance dualism distinguishes itself from Cartesian substance dualism by denying that the body and soul are different substances. Instead, a person is composed of only one substance, the soul, while the body is considered an ensouled physical structure. J. P. Moreland has commented:
Eleonore Stump has suggested that Thomas Aquinas's views on matter and the soul are difficult to define in contemporary discussion but he would fit the criteria as a non-Cartesian substance dualist.
Other terms for Thomistic dualism include hylomorphic dualism or Thomistic hylomorphism which are contrasted with substance dualism. Hylomorphism is distinct from substance dualism as it holds the view that the immaterial and material are not distinct substances and only share an efficient causality.
Thomistic scholars such as Paul Chutikorn and Edward Feser have written that Aquinas was not a substance dualist. Edward Feser who has defended hylomorphic dualism has suggested that it has advantages over substance dualism such as offering a possible solution to the interaction problem. Paul Chutikorn has commented that "adopting Aquinas' view of substance will provide a solution to the problem by avoiding altogether the position that man is made up of dual substances. Rather, Aquinas shows us that we can acknowledge a duality within substance itself, while maintaining its inherent substantial unity".
Aristotelian hylomorphic dualism also has many similarities with Thomistic dualism. Michael Egnor is a notable advocate of Aristotelian dualism.
Property dualism
Property dualism asserts that an ontological distinction lies in the differences between properties of mind and matter, and that consciousness may be ontologically irreducible to neurobiology and physics. It asserts that when matter is organized in the appropriate way, mental properties emerge. Hence, it is a sub-branch of emergent materialism. What views properly fall under the property dualism rubric is itself a matter of dispute. There are different versions of property dualism, some of which claim independent categorisation.Non-reductive physicalism is a form of property dualism in which it is asserted that all mental states are causally reducible to physical states. One argument for this has been made in the form of anomalous monism expressed by Donald Davidson, where it is argued that mental events are identical to physical events, however, strict law-governed causal relationships cannot describe relations of mental events. Another argument for this has been expressed by John Searle, who is the advocate of a distinctive form of physicalism he calls biological naturalism. His view is that although mental states are ontologically irreducible to physical states, they are causally reducible. He has acknowledged that "to many people" his views and those of property dualists look a lot alike, but he thinks the comparison is misleading.
Epiphenomenalism
Epiphenomenalism is a form of property dualism, in which it is asserted that one or more mental states do not have any influence on physical states. It asserts that while material causes give rise to sensations, volitions, ideas, etc., such mental phenomena themselves cause nothing further: they are causal dead-ends. This can be contrasted to interactionism, on the other hand, in which mental causes can produce material effects, and vice versa.Predicate dualism
Predicate dualism is a view espoused by such non-reductive physicalists as Donald Davidson and Jerry Fodor, who maintain that while there is only one ontological category of substances and properties of substances, the predicates that we use to describe mental events cannot be redescribed in terms of physical predicates of natural languages.Predicate dualism is most easily defined as the negation of predicate monism. Predicate monism can be characterized as the view subscribed to by eliminative materialists, who maintain that such intentional predicates as believe, desire, think, feel, etc., will eventually be eliminated from both the language of science and from ordinary language because the entities to which they refer do not exist. Predicate dualists believe that so-called "folk psychology," with all of its propositional attitude ascriptions, is an ineliminable part of the enterprise of describing, explaining, and understanding human mental states and behavior.
For example, Davidson subscribes to anomalous monism, according to which there can be no strict psychophysical laws which connect mental and physical events under their descriptions as mental and physical events. However, all mental events also have physical descriptions. It is in terms of the latter that such events can be connected in law-like relations with other physical events. Mental predicates are irreducibly different in character from physical predicates.