Say hello to Mary – the Zombies’ friend – here to demonstrate that conscious experience cannot be fully explained in physical, scientific terms. By Lisa McLellan
Last week some Zombies suggested that conscious experience may be epiphenomenal. That is to say, it might be a by-product of physical processes, with no causal effect on the physical world. Let us follow this train of thought with a look at Frank Jackson‘s imaginary Mary…
Frank Jackson’s thought experiment:
Imagine a scientist, Mary, who is an expert on the physical processes involved in colour vision. She knows how various surfaces reflect different wavelengths of light, and how this light affects the retina, how this causes signals to be transferred to the visual cortex of the brain, and how these signals are processed. She knows everything there is to know about how the physical processes of colour vision work.
Mary has carried out her extensive research while confined to a black and white room, (or wearing black and white goggles, or with a rare condition which causes her to see only in black and white, depending on which version you prefer). The important point here is that she has never actually experienced colour vision directly. As the thought experiment goes, she is then released from the black and white room (or removes the goggles, or is cured) and for the first time ever, she experiences colour vision. She sees the colour red for the first time.
Does Mary learn something new?
It seems plausible to suggest that she does discover something new. Namely, she discovers what it is like to see the colour red. Jackson argues that Mary learns a new fact about colour vision and, since she already knew all the physical facts about colour vision, this must be a non–physical fact. This implies that not all facts are physical facts.
Could these facts be physical?
This thought experiment rests on the intuition that Mary does not know what it is like to experience the colour red until she is released from her room. Some may deny this. Maybe she could work out what such an experience would be like simply by studying in depth the physical processes involved.
Though I find this unlikely, future scientific discoveries may make this more plausible. We cannot be certain what Mary would know, given a full and complete understanding of the workings of the human brain. It may be that this new physical information would indeed provide a full, scientific description of the subjective nature of conscious experiences. However, I personally am not convinced.
Arguments for non-physical facts –
The case for non-physical facts is emphasised by Thomas Nagel, who argues that we do not know what it is like to be a bat. We could learn everything there is to know about bats, how bats use echolocation to detect surrounding objects, but we would still not know what it is like to be a bat.
Equally, Mary might study pain, learning everything there is to know about the bodily reaction to physical damage. She might understand how the nerves in the finger react to a paper cut, and how they transfer this information to the brain, and how the brain then process this information. She might learn that this would result in an unpleasant sensation. She may even deduce that such a sensation would be sharp and acute, as opposed to a dull throb.
Even so, it seems to me that she could still not understand precisely what it is like to have a paper cut until she gets one. It seems equally unlikely that she would be able to understand the nature of the visual experience of red simply through studying these processes.
So it seems that Mary might indeed learn something new when she walks out of her black and white room: her scientific understanding of colour does not describe the experience of colour fully.
Mary’s experience as epiphenomenal: wrapping up the zombie
Now let us extend the example of Mary to involve not just colour vision, but all conscious experience. If Mary is studying the actions of zombies, she might have a full and complete understanding of the physical workings of a zombie. As philosophical zombies are physically and functionally identical to humans this would also constitute a full and complete understanding of the physical working of a human. If she cannot deduce what it is like to be a human (having conscious experiences) from her investigation of zombies (not having conscious experiences) then she would be unable to tell whether a creature she was examining was a human or a zombie. If asked to describe how humans behave she would feel no need to invoke the conscious experiences that she knows nothing of in order to causally explain human behaviour.
So conscious experience not only cannot be described in physical terms but has no physical effects. It is a by-product of perception – though as to what it does or why it occurs we still are none the wiser.