Mind-body problem

The mind-body problem is a philosophical questioning of the type of relationship the mind has with the body, especially with the brain. Although this problem may have already arisen since the first developments of philosophy, in Plato in particular, and it found its modern formulation as early as the 17th century, it was only during the 20th century that it was explicitly put forward as a fundamental question, even as the central question of the philosophy of the mind under the expression of mind-body problem. This is also referred to as the “mind-body dichotomy“.

It is on the apparent observation that body and mind differ and that they interact together that lies the historical starting point of the mind-body problem. The main theoretical obstacle to understanding this interaction is that of “causal exclusion” from the physical realm, also called “causal completeness”: if physical processes, such as those that take place in our body or our brain, have only physical causes or effects, then they cannot have properly mental causes or effects on the mind. This difficulty in conceiving of the interaction between body and mind first constituted the heart of the problem faced by philosophers of the mind since Descartes. From the 19th century, another essential question concerning the mind-body relationship arose within the framework of materialism: how to conceive of the specificity of the mind in relation to the body if the mind is nothing but a physical process?

The mind-body problem arises today within a new disciplinary field, that of the philosophy of mind, which constitutes one of the main branches of analytic philosophy. By “mind” is meant the set of mental states or processes attributed to human beings and sentient or intelligent organisms. Among the different kinds of mental states, we can distinguish emotions, sensations, perceptions, imaginary representations, beliefs, volitions (like desires). These states seem to possess two major characteristic features: “lived experience”, experienced subjectively and qualitatively, and intentionality. The intentionality of a mental state consists in the fact of bearing on something, of having something as its object. Some mental states have a representative dimension in this sense. At the other pole of the problem, it is necessary to understand by “body” the set of physical states which are correlated to these mental states, without prejudging the nature of this correlation. The notion of body generally refers in this context to what happens in the brain.

(Illustration by René Descartes of reflex activity. Sensory inputs are transmitted through the sensory organs to the pineal gland in the brain and then to the immaterial spirit.)

In philosophy of mind, the problem posed by the nature of the relations between the spirit and the body is partly linked to the difficulty of explaining the relations which exist between the physical states which are realized in the brain and the mental states which are matters of consciousness. However, the mind-body problem covers a broader field of questioning than that corresponding to the “difficult problem of consciousness”, a problem which concerns only the subjective and qualitative aspects of experience, and should therefore not be confused with it. It also raises the essential question of the normative character of the mind and the actions associated with it.

The mind-body problem

Problem statements

Body and mind are different

The experience we have of ourselves makes us perceive sensations, thoughts and actions that we generally attribute to ourselves and which seem to characterize us in an essential way. Such an experience of ourselves prompts us intuitively to make a distinction between our mental states and the physical states of our environment or our body. The former, unlike the latter, appear to involve “lived” experiences, experienced subjectively, and to be “intentional” in character. Indeed, it seems that mental states are experienced in a private and personal mode, while physical states, by their exteriority and their public aspect, appear as objective. It also seems that mental states are intentional in the sense that they are directed towards something they represent, including in the case of imaginary representations. For their part, the physical states are not characterized as such in this way, and maintain between them causal relations which differ from the relations between them that the intentional states or the representations maintain. Nor do they seem to define us in an essential way, and we have the feeling of escaping the type of determinism that governs them.

Normativity is an important characteristic usually attributed specifically to mental states. Our beliefs, our desires and our acts done voluntarily seem to obey reasons or standards that are not found in physical explanations. These reasons or norms are distinguished as such from the causes that determine our behavior or the physical states in which we find ourselves. They make possible axiological-like statements (moral, political, etc.) about values ​​and what “must be.” Moreover, we spontaneously believe in free will. We believe that, to a certain extent, a person can decide for himself what he wants to do and what he does not want to do. This also applies to the realm of beliefs: we believe that we are free to form our own beliefs, which would make us responsible for them. Physical states, on the other hand, seem to be characterized by determinism: each physical state follows others according to certain well-defined laws. However, neither determinism nor even chance can account for the specificity of free will as we intuit it.

Thus, among the traits most often mentioned to distinguish mental from physical states are the following:

Mental states	Physical states
private, directly accessible	public, not directly accessible
subjective and qualitative (qualia)	objectives and quantitative
intentional, representative	“blind”
explained by reasons	explainable by causes
normative	factual
freely formed	strictly determined

Body and mind interact

Although mental states appear to us different from physical states, the mind does not appear to us as independent of the body and the physical world. Indeed, the experience that we have of ourselves, by which we perceive ourselves as sentient beings, thinking and acting, leads us not only to distinguish between mind and body, but also to think that there is between them something at least similar to a causal link, that there is in short a form of interaction by virtue of which one produces an effect on the other. From this perspective, the mind-body relationship can be characterized as an interaction between two types of reality, with:

1. physical states that cause mental states: specifically, the physical make-up of our environment and body causes perceptions and beliefs about our environment and body, as well as emotions
2. mental states that cause physical states: more specifically, desires or volitions cause certain physical behaviors, namely physical states that are capable of producing the intended effects.

We can add to this that certain mental states seem to cause other mental states (for example my feeling of thirst seems to be the cause of my desire to drink), and this in a different way from the way physical states cause drinking of other physical states. Furthermore, there are often causal or causal-appearing chains that involve both physical and mental states. For example, the excessive heat of the ambient air can be considered to cause me an unpleasant sensation of heat; that my unpleasant feeling of heat causes my desire to cool the surrounding air by turning on the air conditioner; that this desire prompts me to press the button on the air conditioning; then, finally, that the cooling of the air produced by the air conditioning causes the disappearance of my unpleasant sensation of heat.

In the causal relationship between mind and body, it is the mind⇒body causality that is central to the concerns associated with the mind-body problem. Indeed, the debate mainly revolves around the question of how it is possible for mental states to cause physical states. Since physical states are known to have causal power, getting a satisfactory answer to this question should resolve the issue of mind⇒body causation.

Physical causality suffices

The success of the modern natural sciences, especially physics, suggests a philosophical principle most often called the “principle of physical completeness”, which is at the heart of the materialist conception of the world and whose first formulation can be found in the 17th century in the English philosopher Thomas Hobbes. The completeness in question concerns both the causes (causal completeness), the laws (nomological completeness) and the explanations (explanatory completeness) of physical states. This principle affirms the following thesis that, insofar as physical states have causes, are subject to laws, and can be explained, then any physical state has complete physical causes, is subject to complete physical laws, and has a complete physical explanation.

In other words, for any physical state, it is never necessary to seek a cause for its production outside the field of study of physics (including matter, forces, space-time). If it is possible to find a causal explanation for any given physical state, then one can discover an explanation that refers exclusively to other physical states, given physical laws. Unlike the previous two statements of the mind-body problem (“mind and body differ” and “mind and body interact”), the principle of physical completeness that “physical causation suffices” is not based on the experience we have of ourselves, but on the results of modern natural science. It is a philosophical thesis based on an extrapolation of the fundamental and universal theories of these sciences.

Several arguments have been put forward in favor of such a principle. One of the most important is based on the fact that modern natural sciences have made available to us, since the appearance of mechanics as a science of movement in the 17th century, fundamental physical theories which are universal, that is, theories whose laws apply to all physical states and systems. However, a universal theory excludes by definition that there are causes, laws or explanations invoking variables which do not appear in these theories, and in particular non-physical causes, laws or explanations. Another important argument is that there would be no empirical evidence that would point to the existence of non-physical causes occurring in nature.

Incompatibility of statements

The mind-body problem consists essentially in the fact that there are good reasons for admitting each of the following three propositions, which, taken together, nevertheless form an inconsistent triad:

1. Mental states are not physical states: mind-body duality principle (1)
2. Mental states cause physical states, and vice versa: principle of mind-body interaction (2)
3. Every physical state has complete physical causes: principle of physical completeness (3)

These three propositions are compatible two by two, but if we do not accept the ad hoc hypothesis of causal overdetermination (according to which mental causality is superimposed on physical causality), each of these pairs of compatible propositions implies the falsity of the third:

• (1) and (2) imply not (3): if mental states are not physical states but cause physical states, then the principle of physical completeness is false (this is the position of interactionist or Cartesian dualism)
• (1) and (3) imply not (2): if mental states are not physical states but any physical state has sufficient physical causes, then a mental state cannot be the cause of a physical state and the mind-body interaction principle is wrong (this is the position of non-interactionist dualism)
• (2) and (3) imply not (1): if mental states cause physical states but all physical states have complete physical causes, then mental states are physical states and the principle of mind-body duality is false (this is the position of materialistic monism or psychophysical identity theory)

In order to resolve the mind-body problem, one must therefore abandon one of the three propositions, thus removing the contradiction which they engender when they are taken simultaneously. Since the first two propositions find their origin in the experience we have of ourselves, and the third is based on the results of modern natural sciences, one may be tempted to consider that the mind-body problem consists of a conflict between our subjective experience and science. But there is also a tension between the first and the second propositions, a tension already noted in the seventeenth century in certain objections made to Descartes and his interactionist dualism. Indeed, the idea that there is a causal link between body and mind seems to be incompatible with the idea that body and mind are radically different.

The proposed solutions

The main conceptions developed in response to the mind-body problem can be grouped into three major tendencies or paradigms:

1. mind-body dualism
2. physicalism
3. panpsychism

Panpsychism is a minority position which is nevertheless experiencing a resurgence of interest and which today distinguishes itself into two main currents: “micropsychism”, for which the constituents of “matter” are entities of a mental nature, and “cosmopsychism”, which identifies the mind with the entire universe. Each of the other two paradigms includes several schools of thought which can be presented schematically as follows:

Branches of mind-body dualism

Interactionist dualism		Non-interactionist dualism
Cartesian dualism	Popperian dualism	Parallelism	Epiphenomenalism

Branches of physicalism

Behaviorism		Reductionism		Functionalism		Eliminativism
Skinner’s theory	Logical behaviorism	Identity of types	Identity of occurrences	Computationalism	Biological functionalism	Spirit elimination	Elimination of qualia

Mind-body dualism is a standard position in philosophy of mind because of its historical importance, but it has few adherents. Often heavily criticized, dualism is generally approached for didactic purposes, especially when it comes to presenting, by contrast, the different forms of physicalism. This position does not necessarily lead to affirming, like Descartes, the existence of two types of substance. There is indeed a “property dualism” for which there is only one type of substance, matter, and which therefore views the mind in terms of specific properties which, although instantiated in a body, are not identifiable with physical properties. Depending on the different approaches, these properties may interact with physical properties, or they may just be epiphenomena; they may also emerge from complex physical properties, or may themselves constitute fundamental properties of nature.

Physicalism, for its part, designates today an ontological position distinct from the methodological physicalism of the Vienna Circle. It covers the set of conceptions for which all entities that exist in the world are ultimately physical entities that can or could, in principle, be described by the physical sciences, and whose causal interactions are completely governed by physical laws. It opposes any form of body-mind dualism and tries to reconcile materialism with mental concepts that fall within our common conception of the mind. The ontological thesis of physicalism that there are only physical entities or properties implies that mental entities, if they exist, have no particular ontological status. This thesis is widely favored in philosophy of mind, but it also has its opponents among authoritative contemporary philosophers of mind such as Thomas Nagel or David Chalmers.

Another way of grouping the main conceptions answering the mind-body problem is to differentiate them according to the type of answer they offer, and to distinguish thus:

• the conceptions which must constitute a solution to the problem, namely mainly dualism, reductionism, functionalism, the theories of emergence
• the conceptions which must lead to the dissolution or even the elimination of the problem, namely eliminativism and panpsychism.

(Includes texts from Wikipedia translated and adapted by Nicolae Sfetcu)