Brian asked:

I’m bringing Bertie’s teapot to earth and placing it on a table. If eight strangers sit around it with pencils and sketchpads and each produces a drawing which, though different from the others because of the angle of view, is consistent with the existence of a teapot created by known human technology, why is this not proof of the physical existence of the teapot?

Answer by Jürgen Lawrenz

I don’t know Bertie; I suppose he is your favourite green Martian. But even if I got this wrong, if he brings an object with him, the situation is clear cut (in short: we are not proposing a Matrix-type illusion or virtual reality, but I’ll discuss this too).

The drawing is prima facie proof that the teapots exists. Eight normally sensitive people with good rendering skills doing it independently of each other leave you no choice but to accept their testimony.

Even more so if you fill the pot with tea and they drink.

All life forms on earth survive on the strength of this sense certainty. Many don’t even have nerves, but still survive because they have other means of ‘proving’ the existence of food and foes, heat and cold etc.

If you programmed a computer to render the teapot it would produce a similar drawing as one of the draughtsmen. If you throw the teapot at the monitor screen you’ll break it.

So this establishes beyond all reasonable doubt the existence of the teapot.

Your question plays on certain dubious theories that are constantly bandied about in the literature of perception which presuppose, without good evidence or sufficient reason, that what we see may not be ‘real’, that all perceptions are manufactured by the brain and that we live in a permanent state of illusion. The thesis of the brain in a vat is of that ilk, and so is the presupposition behind the movie ‘Matrix’.

I don’t wish to sound dogmatic, but the fact is that we don’t have an adequate theory of life, nor an adequate theory of the mind. While this state of affairs persists, anyone can step forward with any conjectures they like. The brain in the vat theory sounds like radical nonsense to me, but you need not take my word for it. Ask any theorist who believes in it to give you a comprehensive account. But you won’t get one, and that’s the real problem.

To return: The proposition that all our perceptions are kinds of illusions is as threadbare of sense as they come. If all humans see objects the same way, then the word ‘illusion’ is meaningless and should be removed from the dictionary. But this is unnecessary because the use of that word in such a context is simply misuse.

What a bat can see may not be ‘real’ in the same way as what you see, but the bat can eat it and so can you, and you will both survive. By eating you prove the existence of whatever food you digest.

It is a different matter if you are asked to give proof of what this food or, in your example, the teapot ‘really’ looks like, independent of the way the draughtsmen and the computer draw it. This is because the teapot produces ‘phenomena’ which your senses pick up. But this is an insignificant problem – even though it seems to bother a lot of people. The point is simply that your eyes can hardly pick up the pot bodily. They can only perceive the radiation reflected from it and manufacture an internal (2D) representation. But you can pick up the pot with your hands (touch); and if you smash it, you can hear the sound.

You see from this that nature has equipped us to perceive RELEVANT information from the teapot to ensure that we perceive something that actually exists, has a certain form, occupies a certain space etc. What is NOT relevant to us for the time being, is its atomic constitution. But we can ascertain this as well, with appropriate technology.

So if you wish to cast doubt on the reliability of our senses to discern real objects, you have to find pseudo-objects. E.g. illusions, hallucinations, virtual reality etc. But these are categorically different kinds of perceptions than those which help you and every creature on earth to orient themselves, navigate and survive.

In sum: Our perceptions are exceptionally reliable. You will find on closer scrutiny of the literature that writers often confuse what your eyes see and your ears hear, with what you judge the phenomenon to have been. If you see the teapot in bad light, you might judge that you are seeing a miniature UFO. But don’t blame your eyes for this! In Shakespeare’s day people used to ‘see’ ghosts. How come we don’t see them any more? It is because ‘seeing’ is a cooperative construct of your eyes and brain; and what your brain makes you ‘see’ can well be a ghost, if you are conditioned to seeing certain phenomena as ghosts. This is what illusionists, virtual realists and other entertainers of this kind exploit. All you need to know about this, however, is that these are peripheral, exceptional cases. If we really were forced to live by them, we would soon be extinct!