Functionalists think that what characterises the nature of the mind is not what it is made from, but what it does. Functionalists therefore change the focus of the philosophy of mind from asking what the mind is made of to, asking what its function is. For example, what makes a mouse trap a mouse trap? It is normally made from wood and metal. However it could conceivably be made of plastic. Or even a group of humans could form a mousetrap with their bodies. A mouse trap is not defined by what it is made from, but by what it does – what it’s function is. Functionalists apply this to the mind and so avoid the normal questions of dualism vs physicalism. A functionalist could be a dualist or a physicalist or neither because they could think a mind could be made from physical stuff, mental stuff or neither. As long as something performs the function of a mind, it is a mind.
A function is what something does. What something does is how it behaves under certain conditions. If you input something into it, you get a certain result or output. The total description of a things function is the list of all its possible inputs and the resulting outputs. If you had that list, you would know its total function and therefore you would know what it does and for a functionalist what it therefore is.
So as long as a system performs the same functions as a mind, which means to have the same outputs for the same inputs, it is a mind. It could be a computer, a brain or any other ‘substrate’. As long as the substrate is able to be structured such that it performs the inputs and outputs of a mind, it can be a mind.
One functionalist argument for understanding the mind in this way is the idea of substrate-independence. Functionalism is influenced by theories in computer science and artificial intelligence. It seems at least conceivable for a mind to be simulated on a computer. This means that our mind could exist on a variety of different substrates, making it substrate independent.
The issue of the possibility of a functional duplicate with different qualia (inverted qualia)
It is logically possible for what a person A sees as red, person B sees as blue and what person B sees as red, person A sees as blue. This is called ‘inverted qualia’. If that was true however, there would be no way to tell from their behaviour since they would each agree on what color each object is. The input of looking at a red object would produce the same output of saying ‘I’m seeing a red object’ in both person A and B. So, they are functionally identical. However, they are not identical in their mental qualia. Therefore, there is more to the mind than just function. Therefore, functionalism is false.
Arguably there will in fact be functional differences between person A and B. Red is an energising color, while blue is a relaxing color. This is why doctors make stimulant medication red and depressant medication blue, to add a placebo effect. Therefore, if we created a set of inputs which could indicate that functional difference – such as encouraging person A and B to look at something red and then measuring the levels of their stress hormone in their blood – we should expect the one who really sees blue to have less. Therefore, there is a functional difference and so functionalism is true.
The issue of the possibility of a functional duplicate with no mentality/qualia (Ned Block’s China thought experiment)
Imagine a human body is connected to the whole population of china instead of a brain. The population of China is similar to the number of neurons in your brain. Imagine Chinese people, linked to each other with radios and microphones, each performed the function of what a neuron would do. The population of china collectively should then be able to replicate the function of a human mind. Block’s point is that this is a functional duplicate of a mind, so according to functionalism it should be a mind. Yet it’s hard to see how that mind would have qualia and so it’s hard to see how it could be a mind. Therefore, functionalism is false.
The functionalist response is that this ‘Chinese mind’ isn’t functionally identical to a normal human mind as its function can be affected by things like electrical interference or batteries running out.
Block argues this is irrelevant. If those disruptions occurred, then it would indeed no longer be a functional duplicate. However, it’s logically possible that such disruptions wouldn’t occur in which case it is a functional duplicate.
Functionalism isn’t committed to the view that anything can become a mind – only substrates which are capable of performing the functional role of a mind. So, the functionalist could argue that people with radios and microphones are insufficient in structure to perform the function of a neuron. Whatever technology is required to give the Chinese people in order to enable them to become functional duplicates of neurons is currently unimaginable and so for all we know might indeed be the sort of thing that could create a conscious mind.
Alternatively, functionalism could be combined with either eliminative materialism or type-identity theory to solve the problem.