From the study of visual illusions we know that our sense of sight can be fooled. The same is true of all of our other senses and this is one of the problems of empirical knowledge. However, there are several other fundamental problems too.


The Limitations of the Senses

Both sounds and light can be represented as waves with particular frequencies (we ignore for these purposes, the fact that light and sound are fundamentally different quantities). Broadly speaking, we see light between 4 x1014 Hz and 9 x 1014 Hz, and we hear sounds between 20 Hz and 20,000 Hz. However sound and light exist at many other frequencies.





1.       Why do you think we are able to see and hear in these particular regions?

2.       Some animals can hear / see other frequencies of sound / light. What do you think life must be like for them?

3.       How do you think this idea translates to the senses of touch, smell and taste?

4.       What implications does this kind of thinking have for what we know about the world?


We have so far considered familiar senses, but it is obvious that there are several other senses in the animal kingdom. Bats emit high-pitched sounds and use the echoes to locate objects ¡V they can literally hear where things are.


Recent research shows that sharks have lateral lines which are sensitive to the electric fields around them. They can sense the electric fields of prey which are totally motionless and hidden under the sand.


Ants and other insects are believed to have great chemical sensitivity (combing touch, taste and smell in some unimaginable way); birds are believed to find their way home following the Earth¡¦s magnetic field; Sargasso eels return by an unknown sense to the St. Lawrence and other rivers which their ancestors knew, but which they themselves have never seen.



1.       Imagine you possessed a chemical sense. You can sense in people nearby, hundreds of aromas in their clothes, levels of adrenaline and other hormones in their sweat and so on. You are in fact a walking forensics lab. What would the world be like for you?

2.       Can you think of any other senses which animals (or aliens) might have?

3.       What implications does this sort of thinking have for how we acquire knowledge about the world?



We Never See the World


You have a big, bright green apple. But no matter how hard you look at it, no matter what you do, you can¡¦t see it. How can this be?


The answer is surprisingly simple, but has profound consequences. When you look at the apple a stream of reflected light hits your eyes. What has happened is that ¡¥white¡¦ light (made up of every colour) has hit the apple, and the apple has absorbed all except the green light, which it has reflected. You therefore see only reflected light, not the object itself. In fact how could you see an apple? Would you have an apple in your eye? It¡¦s a ridiculous idea.


So you can only see light. But what is light? Well, the best we can say is that light is made up of electromagnetic waves that travel at about 300,000 metres per second. And the important point is that light itself is colourless. However, the human eye is stimulated by certain types of light, and the eye in turn stimulates certain areas of the brain, and we somehow (there¡¦s a great mystery here that goes by the name of consciousness) interpret these simulations as colour.


So what can we conclude? There are two facts of great significance:

1.       Colour is an experience in our minds. It is the finale to a complicated process, involving the energy in light being converted in the eye to electrical energy in the brain.

2.       There is no colour in the world of things and objects. That apple only appears to be green; the sky only appears to be blue; there are no colours in the rainbow.


These are deeply disturbing findings, and at first almost impossible to accept. Note that statement two does not mean that the world is black and white. It means that there are no colours ¡V black and white included. We immediately find that this is almost incomprehensible, but we must remember that perceiving colour is ¡¥just¡¦ a conversion of energy from light to electrical energy in the brain. Similarly our sensation of smell is the result of a chemical reaction in the lining of our nose.


So our senses are really only showing us appearances, not reality in any sense. Note that our language is a part of the problem. When we say ¡¥The apple is green,¡¦ the subject of the sentence is the noun apple and the adjective green modifies the noun and the is clearly attaches the quality of greenness to the subject apple. It is perhaps to be expected that our language would reflect the deception of our senses. Language crystallises the deception, as it were, and reflects it back to us, reinforcing our belief that the quality green does, in fact, belong to the object. Such is the ¡¥tyranny of language.¡¦


So the result of all this is that we have no access to the ¡¥real¡¦ world because all we can perceive, all that we can find out, comes to us via our sense, and so is merely the appearance of the thing, not how the thing ¡¥really is¡¦. Plato said that we see only shadows of reality which may be different to the real thing and anyone with any curiosity would wonder what the reality is ¡K


To say that we are being deceived seems like a suspicious way of looking at it. After all, none of our senses intend to deceive us! The truth is, of course, that our senses have evolved with us, and they allow us to make sense of the environment. Notice the phrase make sense, not find sense. We literally make sense of the world ¡V it does not come pre-packaged in sensible parts. There are many possible senses, and our view of the world is at least partly constrained and limited by the particular ones we have. Using these senses the mind manufactures experience, with our senses giving us the kind of information we need to survive. What else could we ask of them?



1.       Where do smells and tastes exist?

2.       There is an old riddle that asks ¡¥Doe a tree in a forest make a noicse when it falls if there is nobody there to hear it?¡¦ What do you think?

3.       Given that our senses can only tell us about the appearance of objects, what can we say about the objects themselves? How can we find out about the ¡¥real apple¡¦ rather than the shiny green and almost spherical object that appears to our senses?