Multiple realizability

The reference to the multiple realization contributes to a classic argument in the philosophy of mind. This argument deals with the Multirealisierbarkeit mental states. Here is the crucial trigger for the transition from the identity theory to find functionalism. The classic formulation of the argument about the multiple realization comes from Hilary Putnam ( Section 1). Jerry Fodor has generalized the argument and with him against an exaggerated reductionism and for independence of the individual sciences argued ( Section 2).

Multiple realization (or the Multirealisierbarkeit mental states ) as an argument against the identity theory

The identity theory

The identity theory is in a well- localized point in the history of philosophy of mind: it is the immediate reaction to the failure of behaviorism, as he was represented approximately by Carl Gustav Hempel or Gilbert Ryle. The lesson that has been learned from this failure was: mental states is get at not only by behavioral descriptions. But what can be mental states?

The obvious answer to the identity theorist is: " Mental states are identical to brain states. " For every mental state M ( ie about headache ) there should be a brain state G, the M is identical. Here, M and G to be understood as types. The type " headache " refers to headaches as a general concept and not a single headache (which are the token). The thesis is thus that M- types are identical to G grades.

The objection

Hilary Putnam (1967 ) developed the first time the argument of multiple realizability, which should show that a mental state can not be identical with a brain state: to be realized, the individual, concrete mental states ( the token) can in fact in different beings throughout different brain states. Just think of the pain of a lurches and a human being. It's just unlikely to run in them the same brain processes when they feel pain. It could be that pain in humans can be realized by the firing of C- fibers in amphibians, however, entirely by something else. However, amphibians and people may have pain. So you have the same mental states, but different brain states. So can mental states (M- types ) may not be identical to brain states (G- types).

Using this argument, the classical identity theory was considered by many to be refuted. (See, however, Jaegwon Kim 1993. ) Of course you could still accept that M- tokens are identical with G- token. Such a theory was formulated by Donald Davidson about. However, the question remains what the individual M- token holds together, what makes them different instantiations of the same types. The orthodox answer to this question was the functionalism: All of the same M- Token (type ) F realized by the same functional state.

The Multirealisierbarkeit mental states is crucial for the decline of the identity theory, since it makes their empirical content of this dispute. It is now proved that not only unequal beings but also in different people, a certain mental state may be interrelated with different neural states. This can be observed nowadays using positron emission tomography (PET). The PET is used, inter alia, to investigate the functions of the brain and explore. A test person inhaling this radioactive oxygen (or glucose). Thereafter, the concentration of the substance is measured in the different areas of the brain. A larger consumption of the substance can simultaneously connect to a higher neuronal activity. In the more active parts of the brain increased blood circulation takes place. Based on this study, it was found that for different persons to solve the same tasks, though often similar, but hardly identical brain states can be observed. Striking here is also the significant difference in brain activity between men and women.

Moreover, one can observe that change the correlations between mental states and brain states even among individuals in the course of their lives. This may be the result of brain injury, for example. Healthy parts of the brain take over some functions that can no longer exercise the injured part. It sounds pretty unlikely, therefore, that every mental state exactly a neurophysiological state to correspond to. The result is a rather weak empirical basis for the identity theory, since the presupposed natural law correlation is lacking.

Multiple realization as an argument against reductionism

It is often assumed that the multiple realization not only provides an argument against the identity theory, but does generally unsatisfactory reductionist positions. It is especially Jerry Fodor (1974 ) have been, who generalizes the argument of multiple realizability. He is of the opinion that the argument shows that the special sciences (such as psychology or economics) to be granted autonomous status from physics. The laws of the special sciences are on principle not due to laws of physics.

This is due Fodor as follows:

Think of a trivial psychological law: "If XY hates, then XY will not kiss - unless X expects any benefits from it." When the argument of multiple realizability is true, so there is no physical law, the psychological to the reduce law would: Because " hate " can be implemented quite differently in different people, so that the cases can no longer be recognized as belonging together in physical language.

Perhaps an even more obvious example is the economy. This can be illustrated with reference to Gresham's law. If the value ratio between several currencies fixed by law, the stronger currency displaces the worse. This law applies regardless of from which the cash is made ​​is or (gold, nickel, mussels, ...), so it is independent of the individual physical realizations. Would we therefore describe only the physical events, so we would not see what all the different cases together. Fodor thinks this, therefore, that any exchange of cash can be described physically though. All these events that may fall under one and the same physical concept of species, however, hardly. Thus, different types of payments can have interesting similarities. This, however, can certainly not be attributed to a single physical description.

Thus follows by Fodor, that can not reasonably be assumed that every single scientific concept of species 'F' just a physical concept of species 'P' can be assigned such that for every single scientific law

( 1) For all x, if x has F, x has also F '

From physics the image law

( 2) For all x, if x has P, x has also P '

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

Thus, it is far more likely that different events in very different ways are physically realized.