Multiple realization

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The reference to the multiple realization adds to a classic argument in the philosophy of mind . This argument deals with the multi-realizability of mental states. This is where the decisive trigger for the transition from identity theory to functionalism can be found. The classic formulation of the multiple realization argument comes from Hilary Putnam (Section 1). Jerry Fodor generalized the argument and used it to argue against excessive reductionism and for the independence of the individual sciences (Section 2).

Multiple realization (or the multi-realizability of mental states) as an argument against identity theory

The identity theory

The identity theory stands at a well localizable point in the history of the philosophy of mind: It is the immediate reaction to the failure of behaviorism , as advocated by Carl Gustav Hempel or Gilbert Ryle . The lesson that was drawn from this failure was: Mental states cannot be dealt with by describing behavior alone. But what can mental states be?

The obvious answer of the identity theorists is: “Mental states are identical to brain states.” For every mental state M (for example headache) there should be a brain state G with which M is identical. M and G are to be understood as types . The “headache” type means headache as a general concept and not a single headache (these are the tokens ). So the thesis is that M-types are identical to G-types.

The objection

Hilary Putnam (1967) first developed the argument of multiple realizability, which was supposed to show that a mental state cannot be identical to a brain state: The individual, concrete mental states (the tokens) can namely be realized in different beings through very different brain states . Think of the pain of an amphibian and a human . They are just unlikely to have the same brain processes going on when they feel pain. It could be that pain is realized in humans by firing C-fibers, but in amphibians by something completely different. Still, amphibians and humans can be in pain. So they have the same mental states but different brain states. So mental states (M types) cannot be identical to brain states (G types).

With this argument, the classic identity theory was considered by many to be refuted. (Compare, however, Jaegwon Kim 1993.) Of course, one could still assume that M tokens are identical to G tokens. Such a theory was formulated by Donald Davidson , for example . The question remains, however, what holds the individual M-Token together, what makes them different instantiations of the same type. The orthodox answer to this question was functionalism : all M-tokens of the same type are realized by the same functional state (type) F.

The multi-realizability of mental states is decisive for the decline of identity theory, as it makes it controversial for its empirical content. In the meantime it has been proven that not only in different beings, but also in different people, a certain mental state can also be interrelated with different neuronal states. Nowadays this can be observed with the help of positron emission tomography (PET). The PET is u. a. used to study and research the functions of the brain. For this purpose, a test person inhales radioactive oxygen (or glucose). Then the concentration of the substance is measured in the different areas of the brain. At the same time, greater consumption of the substance suggests greater neuronal activity. There is higher blood flow in the more active parts of the brain. On the basis of this investigation it could be established that in different people who are supposed to solve the same tasks, similar but hardly identical brain states can often be observed. The considerable difference in brain activity between men and women is also striking.

In addition, it can be observed that the correlations between mental states and brain states change in the course of their lives even in individual people. This can e.g. B. be the result of a brain injury. Healthy parts of the brain sometimes take on functions that the damaged part can no longer perform. It therefore sounds rather unlikely that exactly one neurophysiological state should correspond to every mental state. The result is a rather weak empirical basis for the identity theory, since the natural law correlation to be assumed is missing.

Multiple realization as an argument against reductionism

It is often assumed that multiple realization not only offers an argument against identity theory, but makes reductionist positions generally unsatisfactory. It was particularly Jerry Fodor (1974) who generalized the argument of multiple feasibility. He is of the opinion that the argument shows that the individual sciences (such as psychology or economics ) should be given an autonomous status compared to physics . In principle, the laws of the individual sciences cannot be traced back to the laws of physics.

Fodor justifies this as follows:

  1. Generalizations about events can easily be formulated without their physical descriptions having to have anything in common.
  2. The question of the physical descriptions is often even irrelevant for the truth and interest of the generalizations or for their epistemologically important properties.
  3. For the most part, the individual sciences also deal with generalizations of the above. Art.

Let us think of a trivial psychological law: "If X hates Y, then X will not kiss - unless X expects some benefit from it." If the argument of multiple feasibility is correct, then there is no physical law on which the psychological one is based Law could be reduced: Because "hate" can be realized very differently in different people, so that the cases can no longer be recognized in physical language as belonging together.

Perhaps an even more obvious example is economics. This can be illustrated using Gresham's Law. If the value ratio between several currencies is set by law, the stronger currency displaces the worse. This law applies regardless of what the means of payment consists of or is made of (gold, nickel, shells, ...), so it is independent of the individual physical realizations. So if we were only to describe the physical occurrence, we would not even see what holds all the different cases together. Fodor therefore means that every exchange of means of payment can be described physically. However, all these events can hardly fall under the same physical concept of species. Accordingly, different types of payment transactions can have interesting similarities. However, these can certainly not be traced back to a single physical description.

According to Fodor, it follows that it cannot reasonably be assumed that every single scientific species concept 'F' can be assigned exactly one physical species concept 'P' in such a way that it corresponds to every single scientific law

(1) For all x: If x has F, then x also has F '

the law of images from physics

(2) For all x: If x has P, then x also has P '

can be derived. (→ see: Beckermann, p. 140)

It is therefore far more likely that different events are physically realized in very different ways.

literature

  • Jerry Fodor: Special sciences , in: Synthesis 28 (1974) pp. 97-115
  • Jaegwon Kim: Supervenience and Mind. Selected Philosophical Essays , Cambridge University Press, Cambridge 1993
  • Hilary Putnam : Psychological Predicates , in: WH Captain (Ed.): Art, Mind and Religion , Pittsburgh 1967, pp. 37-48
  • Ansgar Beckermann : Analytical Introduction to the Philosophy of Mind , 2nd edition, de Gruyter, Berlin and New York 2001

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