Sweet and sour

Can objective science explain subjective taste?

Introduction

Our subjective experience includes not just what we can touch and see, but also the taste of food. Can science explain this subjective experience?

Stinky tofu is a Chinese delicacy with a very pungent smell. Some people find it revolting but others love it. Some researchers have tried to identify the chemicals responsible for the smell. The predominant volatile compounds include for example indole:

Other compounds include dimethyl trisulfide, phenol, dimethyl disulfide and dimethyl tetrasulfide, etc.

Is this information sufficient for you to know what stinky tofu smells like? Presumbaly only if you already know what those chemical compounds smell like, and you can only know what they smell like by relying on your subjective experience. If you are born without a sense of smell, presumably the scientific information will not be very helpful to you.

Science is supposed to explain different aspects of the world, but scientific theories are based on objective evidence and observations. Can objective science completely explain the subjective aspect of our taste experience? If so, how? If not, does it mean that there is something in the universe that is forever beyond the reach of science?

Physicalism

Physicalism is the thesis that everything in the world is physical. Physical things are things like molecules, atoms, electrons, gravity, light, quarks, and so on.

According to physicalism, all the empirical facts about the world are physical facts. We have lots of complex things in the world like planets, blackholes, mountains, rivers, etc., but ultimately they are all made of physical things. There is nothing else that exists in the universe that is non-physical.

People who accept physicalism are "physicalists". They believe that consciousness is also part of the physical universe. So even our subjective experience of taste is ultimately physical in nature, determined entirely by the neural properties of the brain.

Many people believe that humans beings have souls. Or they believe in the existence of ghosts, spirits, and God. Usually they do not think that these are physical entities. Physicalists would therefore say that there are no such things.

The knowledge argument

In philosophy, there is a very famous knowledge argument against physicalism, put forward by the philosopher Frank Jackson. The argument aims to show that physicalism is false because it cannot account for our subjective experience.

Here is the outline of the argument (we have changed the example in the original argument):

Ageusia is a medical condition where a person lacks the sense of taste. Anosmia is the inability to smell. Imagine a brilliant scientist Mary who has congenital ageusia and anosmia. Food does not taste anything to her, and in particular she has never tasted stinky tofu before.

But Mary is very smart and she became an excellent scientist who knows all the physical facts. We imagine that she can still perform experiments and study the human brain, so she knows exactly what goes on in the brain when people eat and taste food. She might even be able to predict whether they like the food or not based on their brain states.

Still, it seems reasonable to think that Mary still does not know what stinky tofu really tastes like, since she has never experienced it herself.

Now imagine that her inability to smell and taste is just due to some problems with her tongue and nose and a little operation has restored her smell and taste. Would she learn anything new if she were to eat smelly tofu?

Most people would probably say "yes". But if so, that means she has acquired new knowledge, even though before she already has all the physical knowledge in the world. This means that her new knowledge about what smelly tofu tastes like is not physical knowledge. This seems to show that physicalism is false.

The ability reply

There are many responses to the knowledge argument. Many dualists welcome the argument, since many of them think that consciousess is scientifically inexplicable, and depends on the existence of a soul.

Others regard the argument as fallacious, but there is little agreement as to where the argument goes wrong.

One famous criticism of the argument is the ability reply. It says that knowing what an experience is like is an ability, which is not the same as knowledge of facts. Think about learning how to swim. You might know all the facts about swimming and the physics of buoyancy, but all that factual knowledge is not enough to give you the ability to actually swim. This is no way shows that swimming is a supernatural phenomenon. It is just that factual knowledge about swimming is not the same as practical knowledge of swimming.

Similarly, when it comes to Mary, it might be suggested that what Mary lacks is not more factual knowledge, but the specific ability to imagine and recognize the experience of eating smelly tofu. When she knows what smelly tofu tastes like after the operation, she does not learn any new facts, but gain a new ability. This does not show that physicalism is false.

Here is a TED video about the knowledge argument as applied to vision: