The mind-body problem raises the question of the relationship between the human body, the brain in particular, and the mind. Although this problem has existed almost since the beginning of philosophy (see Plato), it has been recognized since the twentieth century as a fundamental question, even as the central question of philosophy of mind under the English expression of mind-body problem. We also speak of mind-body dichotomy.
The mind-body problem is related to the difficulty of explaining the relationships between physical states or processes that occur in the brain, and states or mental processes, especially those of consciousness. It is scientifically attested that our sensory experiences are caused by stimuli that come to us from the outside world through our sense organs. It is also attested, conversely, that we can move our body so as to satisfy a need or desire of the spirit. The body and the mind interact. The main theoretical obstacle to understand this interaction is that of the “causal exclusion” of the physical domain: if the physical processes, such as those that occur in our body or our brain, have no causes or effects except the physical, then they can not have effects on the mind or causes properly mental.
The question of the interaction between the body and the mind is one of the main questions faced by philosophers of the mind since Descartes. Another essential question concerning the mind-body relation arises in the context of materialism: how to conceive the specificity of the mind in relation to the body if the mind is nothing other than a physical process?
Thales is sometimes considered to be an entirely monistic physicalist, as the opposition between matter and spirit does not exist in this thought. On the other hand, Parmenides notes an insurmountable difference between being and thought on the one hand, and nature on the other; Pythagorism then, imported into Greece the belief in the immortality of the soul, and hence a possible independence of soul and body; Democritus, in a manner somewhat similar to Parmenides, separates what is known by reason and the “conventional” phenomena we observe; finally, Plato is the first philosopher to formulate the problem in all its magnitude by exposing several theories aiming to understand the nature of the soul.
During the 8th Council of Constantinople in 869 (Constantinople IV), it was decreed the suppression of the spirit in the 11th canon, the soul now having a spiritual part. It is from this period that dates the confusion between soul and spirit. Previously, mind was associated with thought and soul with feeling. The trichotomy (body, soul and spirit) has been replaced by the dichotomy (body and soul). We have thus gone from a vision of man in which the soul balances the conflict between body and mind with a vision in which the body harmonizes with the soul or the spirit.
Dualism is thought that admits the existence of both the material world and the spirit, but as different realities by nature. Non-dualistic theories, in the strict sense, may not be reductionist, that is to say, admit the existence of the material world and the mind, but without lending them any substantial difference other than a difference of categories.
In the case of dualism, the classic problem is that of the relations between these two worlds: the typology of dualism shows the different ways of responding to this problem. In general, dualist thinkers admit the obscurity of these relationships (Descartes) – but by asking the evidence of its existence (we experience that we have a double existence), or resort to a transcendent causality to the experience that is either the direct action of God (Nicolas Malebranche), or a consequence of the action of God organizing the world (Gottfried Wilhelm Leibniz).
Dualism is characterized by the following traits: the body is localized in space and time; it can be known by the senses, and it can be the object of the sciences which seek its causal mechanisms; the mind (or the soul), on the other hand, is localized in an interiority that is neither visible nor, consequently, recognizable by others: the mind can not therefore be the object of a science, for it escapes the causal existence of matter. The impossibility of dualism to attest to the existence of the spirit of others often leads to a second aporia: solipsism.
According to René Descartes, body and soul are two “really distinct” substances: indeed, we can have a clear and distinct knowledge of one without having to conceive the other (Principes de la philosophie, I, 60 ). The soul is a thinking substance, while the body is an extended substance (which extends into space). However, this real distinction of body and soul is not opposed to their union, Cartesian “dualism” does not mean that soul and body are completely separate: there are thus “certain things that we experience in ourselves. themselves, which should not be attributed to the soul alone, nor to the body alone, but to the close union that is between them … such are the appetites for drinking, eating, and emotions or passions of the soul, which do not depend on thought alone, such as emotion to anger, joy, sadness, love, a.s.o., such are all the feelings, such as light, colors, sounds, smells, taste, warmth, harshness, and all the other qualities which fall only in the sense of touching.“ (Principes de la philosophie, I, 48).
The union of the soul and the body is a mystery: we can not know it clearly and distinctly, that is, we do not understand it; but we experience it with evidence. It is therefore impossible for us to think of the union of body and mind. We can only live it. Descartes thought that the place of union of body and mind was in the pineal gland.