What exactly is functionalism, and how do functionalists appeal to the notion of multiple realisability to motivate their view, especially in response to identity theory? How in particular is functionalism meant to be an improvement over behaviourism?
Functionalism is a theory in contemporary philosophy of mind, which is regarded as another choice between identity theory and behaviourism, focusing on the traditional mind-body problem. The key claim of functionalism is that ‘mental states are characterized by their causal role’, and the word ‘causal role’ represents a ‘functional role’, a mental state, linked with physical, sensory input, and behaviours or other mental states output. For example, imagine a piece of glass is being knocked by a hammer, and it breaks into pieces. In this process, knocking is a physical input and ‘break’ is the final output. The direct reason causes the break is the fragility of the glass, which can be considered an abstract causal role. Although according to chemistry, the fragility of glass can be explained by its structure properties, physical causation and functional role are still different concepts.
As an extension to this example, we replace the hammer with a nail, the glass represents the physical body and the break of glass represents the scream direct after the hurt. The scream itself is directly caused by the pain – an abstract, functional role which may have a causal relationship to the brain but still act in a different role.
In functionalism’s concern, mental states can be understood without considering the physical state, as it believes that mental states are not related to one specialized physical behaviour, they can be realized and interpreted in multiple ways, and this is called multiple realisability. The concept of multiple realisability is a response to Jack Smart’s identity theory to some degree. According to identity theory, mental states are nothing but physical (especially the brain) states and behaviour facts (Smart, p.143). For example, when getting hurt physically, naturally people feel pain instantly and they will scream or do other behaviours. In neuroscience, neuropathic pain is caused by C-fibre activation, as the activation itself is considered as pain or something equal to pain in identity theory. However, according to functionalism, pain is a functional state of the organism (Putnam, p.200). If an individual’s nerves are too blunt to feel the pain, or the individual is abnormal enough to feel excited about being hurt, the C-fibre activation itself will not be regarded as pain – at least not in their inner thinking process (Putnam, p.202). For functionalism, differences between realizing processes are important evidence to determine the mental state as a functional role between sensory input and following behaviours.
Functionalism is usually regarded as an improved version of behaviourism, which believes mental states are nothing but expressed physical behaviours. Both of them emphasise the practical part of a mental state and functionalism ‘inherits’ behaviourism’s focus on an individual’s expression – physically or mentally. Compared to behaviourism, functionalism affirms the effect of the inner process and proposes that the same mental state can act in different functional roles, hence leading to other different mental states or behaviours. In functionalism’s concern, physical behaviours can be regarded as relatively independent of mental states, and from this hypothesis, it even can be compatible with dualism (Putnam, p.200). Functionalism’s further extension of the mental state provides a wider, more comprehensive and precise outlook on the mind-body problem.