Mind–body dualism
In the philosophy of mind, mind–body dualism denotes either the view that mental phenomena are non-physical,[1] or that the mind and body are distinct and separable.[2] 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.[1][2]
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,[3][4] whereas there remains an immortal and perpetual intellective part of mind.[5] 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.[6] 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.[7]
Dualism is closely associated with the thought of René Descartes (1641), 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.[8] Hence, he was the first documented Western philosopher to formulate the mind–body problem in the form in which it exists today.[9] 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 emergent materialism or non-reductive physicalism in some sense.
History[edit]
Ancient Greek philosophy[edit]
Hermotimus of Clazomenae (fl. c. 6th century BCE) was a philosopher who first proposed the idea of mind being fundamental in the cause of change.[28] He proposed that physical entities are static, while reason[29] causes the change. Sextus Empiricus places him with Hesiod, Parmenides, and Empedocles, as belonging to the class of philosophers who held a dualistic theory of a material and an active principle being together the origin of the universe.[30] Similar ideas were expounded by Anaxagoras.
In the dialogue Phaedo, Plato formulated his famous Theory of Forms as distinct and immaterial substances of which the objects and other phenomena that we perceive in the world are nothing more than mere shadows.[6]
In the Phaedo, Plato makes it clear that the Forms are the universalia ante res, i.e. they are ideal universals, by which we are able to understand the world. In his allegory of the cave, Plato likens the achievement of philosophical understanding to emerging into the sunlight from a dark cave, where only vague shadows of what lies beyond that prison are cast dimly upon the wall. Plato's forms are non-physical and non-mental. They exist nowhere in time or space, but neither do they exist in the mind, nor in the pleroma of matter; rather, matter is said to "participate" in form (μεθεξις, methexis). It remained unclear however, even to Aristotle, exactly what Plato intended by that.
Aristotle argued at length against many aspects of Plato's forms, creating his own doctrine of hylomorphism wherein form and matter coexist. Ultimately however, Aristotle's aim was to perfect a theory of forms, rather than to reject it. Although Aristotle strongly rejected the independent existence Plato attributed to forms, his metaphysics do agree with Plato's a priori considerations quite often. For example, Aristotle argues that changeless, eternal substantial form is necessarily immaterial. Because matter provides a stable substratum for a change in form, matter always has the potential to change. Thus, if given an eternity in which to do so, it will, necessarily, exercise that potential.
Part of Aristotle's psychology, the study of the soul, is his account of the ability of humans to reason and the ability of animals to perceive. In both cases, perfect copies of forms are acquired, either by direct impression of environmental forms, in the case of perception, or else by virtue of contemplation, understanding and recollection. He believed the mind can literally assume any form being contemplated or experienced, and it was unique in its ability to become a blank slate, having no essential form. As thoughts of earth are not heavy, any more than thoughts of fire are causally efficient, they provide an immaterial complement for the formless mind.[3]
From Neoplatonism to scholasticism[edit]
The philosophical school of Neoplatonism, most active in Late Antiquity, claimed that the physical and the spiritual are both emanations of the One. Neoplatonism exerted a considerable influence on Christianity, as did the philosophy of Aristotle via scholasticism.[31]
In the scholastic tradition of Saint Thomas Aquinas, a number of whose doctrines have been incorporated into Roman Catholic dogma, the soul is the substantial form of a human being.[32] Aquinas held the Quaestiones disputate de anima, or 'Disputed questions on the soul', at the Roman studium provinciale of the Dominican Order at Santa Sabina, the forerunner of the Pontifical University of Saint Thomas Aquinas, Angelicum during the academic year 1265–1266.[33] By 1268 Aquinas had written at least the first book of the Sententia Libri De anima, Aquinas' commentary on Aristotle's De anima, the translation of which from the Greek was completed by Aquinas' Dominican associate at Viterbo, William of Moerbeke in 1267.[34] Like Aristotle, Aquinas held that the human being was a unified composite substance of two substantial principles: form and matter. The soul is the substantial form and so the first actuality of a material organic body with the potentiality for life.[35]
While Aquinas defended the unity of human nature as a composite substance constituted by these two inextricable principles of form and matter, he also argued for the incorruptibility of the intellectual soul,[32] in contrast to the corruptibility of the vegetative and sensitive animation of plants and animals.[32] His argument for the subsistence and incorruptibility of the intellectual soul takes its point of departure from the metaphysical principle that operation follows upon being (agiture sequitur esse), i.e., the activity of a thing reveals the mode of being and existence it depends upon. Since the intellectual soul exercises its own per se intellectual operations without employing material faculties, i.e. intellectual operations are immaterial, the intellect itself and the intellectual soul, must likewise be immaterial and so incorruptible. Even though the intellectual soul of man is able to subsist upon the death of the human being, Aquinas does not hold that the human person is able to remain integrated at death. The separated intellectual soul is neither a man nor a human person. The intellectual soul by itself is not a human person (i.e., an individual supposit of a rational nature).[36] Hence, Aquinas held that "soul of St. Peter pray for us" would be more appropriate than "St. Peter pray for us", because all things connected with his person, including memories, ended with his corporeal life.[37]
The Catholic doctrine of the resurrection of the body does not subscribe that, sees body and soul as forming a whole and states that at the second coming, the souls of the departed will be reunited with their bodies as a whole person (substance) and witness to the apocalypse. The thorough consistency between dogma and contemporary science was maintained here[38] in part from a serious attendance to the principle that there can be only one truth. Consistency with science, logic, philosophy, and faith remained a high priority for centuries, and a university doctorate in theology generally included the entire science curriculum as a prerequisite. This doctrine is not universally accepted by Christians today. Many believe that one's immortal soul goes directly to Heaven upon death of the body.[39]
Descartes and his disciples[edit]
In his Meditations on First Philosophy, René Descartes embarked upon a quest in which he called all his previous beliefs into doubt, in order to find out what he could be certain of.[9] In so doing, he discovered that he could doubt whether he had a body (it could be that he was dreaming of it or that it was an illusion created by an evil demon), but he could not doubt whether he had a mind. This gave Descartes his first inkling that the mind and body were different things. The mind, according to Descartes, was a "thinking thing" (Latin: res cogitans), and an immaterial substance. This "thing" was the essence of himself, that which doubts, believes, hopes, and thinks. The body, "the thing that exists" (res extensa), regulates normal bodily functions (such as heart and liver). According to Descartes, animals only had a body and not a soul (which distinguishes humans from animals). The distinction between mind and body is argued in Meditation VI as follows: I have a clear and distinct idea of myself as a thinking, non-extended thing, and a clear and distinct idea of body as an extended and non-thinking thing. Whatever I can conceive clearly and distinctly, God can so create.
The central claim of what is often called Cartesian dualism, in honor of Descartes, is that the immaterial mind and the material body, while being ontologically distinct substances, causally interact. This is an idea that continues to feature prominently in many non-European philosophies. Mental events cause physical events, and vice versa. But this leads to a substantial problem for Cartesian dualism: How can an immaterial mind cause anything in a material body, and vice versa? This has often been called the "problem of interactionism."
Descartes himself struggled to come up with a feasible answer to this problem. In his letter to Elisabeth of Bohemia, Princess Palatine, he suggested that spirits interacted with the body through the pineal gland, a small gland in the centre of the brain, between the two hemispheres.[9] The term Cartesian dualism is also often associated with this more specific notion of causal interaction through the pineal gland. However, this explanation was not satisfactory: how can an immaterial mind interact with the physical pineal gland? Because Descartes' was such a difficult theory to defend, some of his disciples, such as Arnold Geulincx and Nicolas Malebranche, proposed a different explanation: That all mind–body interactions required the direct intervention of God. According to these philosophers, the appropriate states of mind and body were only the occasions for such intervention, not real causes. These occasionalists maintained the strong thesis that all causation was directly dependent on God, instead of holding that all causation was natural except for that between mind and body.[27]
Recent formulations[edit]
In addition to already discussed theories of dualism (particularly the Christian and Cartesian models) there are new theories in the defense of dualism. Naturalistic dualism comes from Australian philosopher, David Chalmers (born 1966) who argues there is an explanatory gap between objective and subjective experience that cannot be bridged by reductionism because consciousness is, at least, logically autonomous of the physical properties upon which it supervenes. According to Chalmers, a naturalistic account of property dualism requires a new fundamental category of properties described by new laws of supervenience; the challenge being analogous to that of understanding electricity based on the mechanistic and Newtonian models of materialism prior to Maxwell's equations.
A similar defense comes from Australian philosopher Frank Jackson (born 1943) who revived the theory of epiphenomenalism which argues that mental states do not play a role in physical states. Jackson argues that there are two kinds of dualism:
He claims that functions of the mind/soul are internal, very private experiences that are not accessible to observation by others, and therefore not accessible by science (at least not yet). We can know everything, for example, about a bat's facility for echolocation, but we will never know how the bat experiences that phenomenon.
