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Advantages
- Overcomes the problem of neural dependence/consistent with neuroscientific evidence. A key problem with dualism is that it is not consistent with empirical evidence which points to the dependence of the mind on the brain. Conversely, Identity Theory was developed as a result of the growing evidence of the correlation between metal and physical states.
- Overcomes the problem of mental causation. Identity theory is consistent with the Causal Closure of the Physical - if mental events just are physical events, then we can say that mental events cause physical events; there is no problem of interaction to overcome.
- Token Identity Theory: Token Identity theory is able to overcome the problems of individual differences and multiple realisability. This is because it rejects the claim that mental properties are identical to any type of physical state. Instead, every mental property occurs with and because of a physical property, but what occurs with each mental token varies from person to person, creature to creature.. So while in me, pain might occur with C-fibres firing, this could one day change to some other fibre, and pain in an octopus might occur when O-fibres fire.
- Response to the irreducibility of consciousness: First, we can respond to the 'knowledge argument' by questioning whether the knowledge obtained is really propositional knowledge, or whether the acquisition of qualia amounts to 'ability knowledge'. Secondly, Daniel Dennett is able to dismiss the problem of qualia by pointing out that it is a functional property - it can be manipulated by manipulating certain physical properties of the brain, so that it produces different outputs.
- Response to the conceivability argument: Dennett argues that philosophers cannot really conceive of zombies. If a zombie genuinely was functionally identical, it simply could not lack consciousness.. a pre-condition of human-like behaviour = being conscious.
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Disadvantages
- Individual differences - Types of Mental State: can we actually identify mental states of the same type? For example, is my thought 'tea is nice' the same as your thought 'tea is nice'? Mine might be linked to years of tea drinking; yours might have arisen after just a few tea-based experiences. If we can't day what a thought of the same type is, how can we establish type-identity with brain states?
- Individual Differences - Compensation: We know that when an area of the brain is damaged, other parts of the brain compensate. So, even if the neural network which was activated when I first thought 'tea is nice' has been damaged, I can still have a positive thought about Dustin Hoffman! Clearly, the type of thought is not identical to any particularly physical state.
- Multiple Realisability: Hilary Putnam pointed out that if we can find a single psychological predicate which applies to both humans and (for example) an octopus, whose physical-chemical correlate is different, then type identity theory is false. In other words, if pain can be realised by both O and C fibres firing, then pain is not identical to C-fibres firing, becase it is multiply realisable.
- The Irreducibility of Consciousness: This objection points out that conscious mental states involve a subjective point of view of the individual (consider 'What is it Like to be a Bat?'). There is something it is like to be in a particular state (qualia), and this resists reduction. Frank Jackson's Knowledge argument points out that explaining all physical facts leaves out important mental facts.
- The Conceivability Argument: Chalmers argues that it is possible to conceive of a zombies who are physically identical to conscious human beings, but who do not have minds. Given that this is conceivable, it is metaphysically possible. If there could be such a world in which there is no consciousness, despite the physical facts being left intact, then consciousness must be non-physical.
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Evaluation
Type Identity Theory is not tenable: it is undermined by the impossibility of discovering 'types' of mental state, and identifying them with any set type of brain state. However, token identity theory is able to overcome these problems. Furthermore, if we accept the functional account of token identity theory (mental properties = functional properties), then we can argue that irreducible features of consciousness are simply functional properties.
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