When Louis Armstrong (or it may have been Fats Waller) was asked to define jazz, he replied, 'If you've gotta ask, you ain't never gonna know.' He meant that you either immediately recognise what jazz is or you don't; if you don't, it is very difficult to help out by putting into words what it is. Consciousness is much more of a challenge to define than jazz. It is at one and the same time both blindingly obvious and extremely elusive; it is here right before us all the time and yet hardly ever noticed throughout our waking hours. And it seems impossible to pin down in words what consciousness is.

You cannot define it by comparing it to something else that is like it. If I wanted to explain what a spade was, I could begin by talking about tools, gardens, about, forks and hoes and digging. For a spade is part of a world we are familiar with. We can grasp the part a spade plays in it and begin to understand what a spade is. But consciousness cannot be described in that sort of way. It is not part of a wider world that we already understand. It is not really like anything else.

It is difficult enough trying to define a colour. How would we define the word 'red' to someone who had never seen a red object? But at least we could talk about other colours and perhaps, point to a red object and in the hope that the word would begin to make sense. But we have no resources like this to help us define what consciousness is. We cannot point to consciousness.

To my understanding, this is what consciousness is:

1. it is direct, immediate experience (in the sense that no one has to tell me I am conscious: I just know that I am)

2. it is private to me (in the sense that and no one else can have the experience I am having)

3. it occupies the present moment and manifests in many forms:

a) in the experiences of the senses: smelling a honeysuckle; hearing a clarinet; tasting Marmite; feeling wetness or dryness; seeing a tree

b) in feeling pain, from mild aching or throbbing or stinging to excruciating agony

c) in feeling sleepy or hungry or nauseous or itchy

d) in experiences of emotional states: of being angry, of yearning with desire, having the butterflies of fear, knowing the mood of sadness, being embarrassed or hot with rage, being excited, guilty, irritated, regretful, jealous, exasperated, annoyed

e) in experiences of imagining, of remembering, of thinking, calculating a total of numbers, of having an idea occur to you, of speculating about the future, of meditating, pondering, doubting, questioning.

In addition (and in contrast with physical objects) consciousness has no dimensions, no volume, no mass and no location in space. You cannot measure the length of a feeling, the weight of a smell, the volume of a fear. It doesn't make much sense to ask how many centimetres long a taste is or how wide a feeling of rage is or how much a sound weighs.


Think of a camera. You aim it at the tree and press the button. Light enters the camera and leaves an image on light sensitive paper. Now, think about a human act of seeing. We look at a tree. Light reflected from the tree comes into the eye and leaves an image on the retina at the back of the eye. So far a bit like the camera. A great deal more happens next in the brain, and the human brain is vastly more complicated than the most sophisticated camera but they are both physical objects which differ in degree of complexity. But in the case of a human looking at a tree, there is in addition to the mechanics of the eye and brain the conscious experience of seeing the tree. This is a difference not of degree but of quality. It is not the case that there is a simple conscious experience in the camera and a more complex one in the human. The conscious experience has no parallel at all in the camera; there is nothing remotely like it in the camera.

What is this conscious experience of seeing? Where does it come from? Is it just part of the brain that we do not yet understand or is it apart from the brain?

In the case of the camera when you have described the mechanics of how the camera works and what it produces that is the whole story of what is going on there. But if you could describe all the brain events that take place when a human has a conscious experience of seeing, you miss out something extremely significant. Humans have conscious experiences: cameras do not.


Look at this quotation:
‘When I turn my gaze skyward I see the flattened dome of the sky and the sun’s brilliant disc and a hundred other visible things underneath it. What are the steps which bring this about? A pencil of light from the sun enters the eye and is focused there on the retina. It gives rise to a change, which in turn travels to the nerve layer at the top of the brain. The whole chain of these events, from the sun to the top of my brain, is physical. Each step is an electrical reaction. But now there succeeds a change wholly unlike any that led up to it, and wholly inexplicable by us. A visual scene presents itself to the mind: I see the dome of the sky and the sun in it, and a hundred other visual things beside. In fact, I perceive a picture of the world around me.’ (from Charles Sherrington, twentieth century neurologist)

What Sherrington is conveying is something like this. When we analyse what happens when we see something, we begin by tracing all the stages of the physical process: the ray of light, the passage through the eye to the retina, the sending of data to the visual cortex at the back of the brain. But at this point an event occurs which does not seem possible to include in this series of physical descriptions. There is an experience of seeing; there is awareness of images. Now this experience or awareness seems to be outside the physical process but, nevertheless, an event about which there cannot be any doubt.How can we account for the arising of consciousness in physical terms? For more on this problem click on VISION


According to its label Marmite contains: yeast extract, salt, vegetable extract, niacin, thiamin, spice extracts, riboflavin, folic acid, celery extract and vitamin B12. It is possible to analyse items on that list in more depth; salt is sodium chloride, riboflavin is a B vitamin and so on. We could continue the breakdown by analysing sodium and chloride and by breaking riboflavin down to its basic chemistry. An expert in food science might know all the available information about the chemical structure of Marmite.

When we eat Marmite, it makes contact with taste buds on the tongue. The tongue has a specialized area for each of the four basic tastes: sweet, sour, salt, bitter. Taste buds are 20 to 40 millionths of an inch wide and contain 30 to 80 receptors which send information via cranial nerves to the brain. Again an expert might know all the available information about how the taste buds work, how they send information to the brain and how the brain processes that information.

Suppose someone has studied both the food science of Marmite and the physiology of taste and knows all that there is to know about what happens when Marmite has made contact with taste buds and the brain has assimilated this data. And suppose also that this person has never actually tasted Marmite. Would he or she on the basis of all the information possessed be able to predict what the taste of Marmite is like?

Intuitively, it seems that the answer is no. Perhaps first we should ask whether this is because the person still lacks some information about the chemical make up of Marmite or about how the taste system works in the brain that would enable them to predict the taste. Imagine, then, that in the future the chemistry of Marmite and the study of the taste system continue to make progress and add even more to the sum of knowledge. Would the future even more knowledgeable expert be in a better position to know, in advance of tasting, what the taste of Marmite is like?

If your answer to this question is no, then it seems that the special and distinctive quality of the taste is not included in the list of physical ingredients. The sense experience of the taste is something that exists over and above the facts of chemistry and brain systems. (This quality is sometimes called the what-it-is-like quality, the phenomenal ‘feel’ or an example of qualia.)

How do we explain what this taste is? Is taste part of the brain in some sense (mind-brain identity theory)? Is it a non-physical substance separate from the brain (substance dualism)? Is it a property of the physical brain (property dualism)? Are there other ways of looking at the problem (behaviourism, functionalism etc.)?

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