Jeffrey asked:

What if every person sees colors different? like, my yellow is someone else’s green, we would never know! and maybe that’s why people have different favorite colors?

Answer by Craig Skinner

This colours argument is one of a number of ‘conceivability’ arguments intended to refute reductionism, that is to combat the notion that the mental is ultimately explicable by the physical.

So, the story goes, we can conceive of a situation where, on our viewing a ripe tomato, identical electrochemical goings-on occur in my brain and your brain, but the mental outcome is that I experience ‘red’ whereas you experience the sensation I do on viewing the sky on a clear sunny day (of course you call this sensation ‘red’ since we all learn that tomatoes are red, skies blue etc). So, the story continues, the quality of conscious experience doesn’t just depend on physical events in a brain interacting with the body and the world.

Another popular conceivability argument is the zombie one. I can conceive of an atom-for-atom duplicate of myself which has brain events identical with mine but totally lacks any consciousness. So, whatever explains consciousness, it isn’t physical events in a brain.

Descartes started it with his ‘clear and distinct’ conception of the separability of the mind and the body, so, he says, mind and body are separate substances (dualism), mind can exist without body etc.

I find these arguments tedious. I have two criticisms:

(1) Just because something is conceivable doesn’t mean its possible. Right now I can conceive of my cat jumping on the desk and deliberately typing in a sparkling finish to this answer. But it won’t. It can’t. Not in any possible world. It doesn’t have the brainpower. Of course in some possible worlds there will be cat-like creatures that can do this, but they won’t be cats as we understand the term ‘cat’.

(2) Advances in scientific understanding will show such arguments to be nonsense. Here are two examples. (a) I can conceive of a gas in which all the particles move faster and faster but the gas’s temperature doesn’t rise. So, whatever temperature increase is, it’s not necessarily to do with speeding up of particles. Wrong. Increase in temperature just IS speeding up of particles. (b) I can conceive of a world containing tiny, replicating bags of chemicals undergoing complex interactions (let’s call them ‘cells’), but these cells are not alive, just little bags of dead chemicals. So, whatever life is, it’s not explained by complex chemical interactions. Wrong. Life just IS complex interaction of dead chemicals in units drawing energy from the environment, maintaining dynamic stability and replicating.

So, I think the colours argument and the zombie argument will likewise be shown to be nonsensical by advances in cognitive science. In the meantime I find it completely implausible that healthy members of the same species would see colours differently. The onus is on those who think otherwise to come up with evidence for their view. And there is none. Or at least none that I find plausible. You suggest people’s having different favourite colours as evidence. Fair enough. Seeing colours differently is a conceivable explanation. But I don’t think it is the most likely one.

Answer by Helier Robinson

It’s not just colours, it’s all sensations: various degrees of hot and cold, rough and smooth, hard and soft, heavy and light, solid and liquid, loud and quiet, penetrability — to say nothing of tastes and smells — all are private to the person concerned. None can be compared to anyone else’s and so could in principle be different among different people. And then there are other animals: what are cats’ and dogs’ sensations like?

This fundamental privacy of sensations leads to a serious philosophical problem. In philosophy everything known through the senses is called empirical, and the world each of us perceives is their empirical world. An empirical world is a structure of empirical objects, which are structures of sensations. A structure is a set of relations holding sensations and objects together. But relations give trouble also: can we perceive them, or are they all in the mind of the perceiver? How can we perceive them if they do not have any empirical qualities, which is to say that they are not composed of sensations? But if they are all in the mind then they are private, just like sensations, in which case each person’s empirical world is private to them. How can this be reconciled with the common sense view that there is only one empirical world, which is real in the sense of continuing to exist when unperceived? The tendency among philosophers these days is to say that ‘somehow’ we perceive reality by means of sensations; the reality is one and public, the sensations are many and private. But in my (minority) view this is a cop out. Try to see if you can figure it out for yourself.