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Does the world exist? The answer to that question seems to be quite obvious: ‘Of course the world exists! I am reading this worksheet right now!’ Well, imagine this:

Suppose you were just a brain-in-a-vat (like a large tank, or tub). All your experiences and senses are given to you by some mad scientist through the vat-machine. Everything that you see, hear, feel, touch and taste do not really exist, they only seem to exist – in truth, they are just chemical/electrical impulses.

What is the difference, in terms of your experience of the world, between you living in a brain-in-a-vat and you living in the real world? There is no difference. If you were a brain-in-a-vat, then you would not even know that you are a brain-in-a-vat. Since there is no difference in terms of experience, the inference from ‘me viewing this worksheet’ to there being a real world which we know, does not follow. We cannot use that as a reason to support the view we know that the world exists!

So, what do we do? Do we give up and believe that everything that we have seen is false? Are we merely plugged into a machine? Are we alone in all of existence? Surely not! This is one of the many tasks of a philosopher, when presented with difficult and mindboggling problems, the job is to try our best to solve them.

Scepticism is questioning the possibility of knowledge. In this worksheet, I will go through the history of scepticism and present different solutions to this problem throughout history and prod your mind to think about these solutions, whether they are satisfactory or not.

So, let us look at the history of this problem:

We begin in Ancient China, in the 5^th century BC. A philosopher named Zhuang Zhou decides to sleep for a while…

昔者莊周夢為胡蝶，栩栩然胡蝶也，自喻適志與。不知周也。
Once, Zhuang Zhou dreamed he was a butterfly, a butterfly flitting and fluttering about, happy with himself and doing as he pleased. He didn’t know that he was Zhuang Zhou.

俄然覺，則蘧蘧然周也。不知周之夢為胡蝶與，胡蝶之夢為周與。周與胡蝶，則必有分矣。此之謂物化。
Suddenly he woke up and there he was, solid and unmistakable Zhuang Zhou. But he didn’t know if he was Zhuang Zhou who had dreamt he was a butterfly, or a butterfly dreaming that he was Zhuang Zhou. Between Zhuang Zhou and the butterfly there must be some distinction! This is called the Transformation of Things.

Zhuang Zhou, Zhuangzi, Ch. II

We now go to France in the 17^th century with Rene Descartes. Here is where the modern understanding of scepticism begins. This is how he intends to doubt everything:

So today I have expressly rid my mind of all worries and arranged for myself a clear stretch of free time. I am here quite alone, and at last I will devote myself sincerely and without reservation to the general demolition of my opinions. But to accomplish this, it will not be necessary for me to show that all my opinions are false, which is something I could perhaps never manage. Reason now leads me to think that I should hold back my assent from opinions which are not completely certain and indubitable just as carefully as I do from those which are patently false. So, for the purpose of rejecting all my opinions, it will be enough if I find in each of them at least some reason for doubt. And to do this I will not need to run through them all individually, which would be an endless task. Once the foundations of a building are undermined, anything built on them collapses of its own accord; so, I will go straight for the basic principles on which all my former beliefs rested.

Rene Descartes, Meditations, Ch. I

There are two principles upon which these beliefs rest upon:

• Experience – like seeing people move and walk.
• Reason – like knowing that 1+1=2

Descartes challenges experience in much the same way as Zhuang Zhou does, proposing that one could just be dreaming everything that they are experiencing now. Therefore, one cannot rest their beliefs on what they see, smell, hear, feel and touch. Reason still survives, though! Reason captures knowledge in the same way as mathematics. I do not need to leave my seat and have experiences, to know things about maths.

However, Descartes provides for us a way to doubt the truth of maths also. Suppose that instead of God, there was an evil demon who not only fools us into thinking that the external world exists, but that truths like 1+1=2 is the case. In this case, I do not know if 1+1=2 is true, and I don’t know if the sky is blue either. Both bases of knowledge have been undermined.

With that, Descartes concludes that you can only be certain of at least one thing.
That you exist. He considers this line of thought:

1 – I am doubting everything.

2 – Doubting is part of thinking.

3 – If I think, then I must exist (since there must be an ‘I’ to think in the first place).

C – I think, therefore, I exist. Or I think therefore, I am.

Well, this might save us from entering a complete spiral where we do not know even if we exist. But let us see if we can rebuild our world from here. Descartes’ solution is this:

1 – I have a “strong inclination” to believe in the reality of the external world due to my senses.

2 – God must have created me with this nature.

3 – If the external world does not exist, God is a deceiver.

4 – But God is not a deceiver.

5 – So, the external world exists

Well, here we have a way out. God will not deceive us into believing false things, so the external world must be a true thing, unless God is tricking us!

Many people might already dispute God’s existence, so it seems there are parts of this argument which seem to not be acceptable to everyone. Perhaps we can find something else to help us.

Let’s go back to the Brain-In-a-Vat case. Maybe we can find a better argument there. God might help us a little, but maybe we can rely on something else for grounding our belief in the existence of the external world.

Hilary Putnam – His argument goes as follows:

1 –  If I am a Brain-in-a-vat, then my word ‘tree’
does not refer to trees.

2 – My word ‘tree’ refers to trees. So,

3 – I am not a brain-in-a-vat. [(A),(B)]

For Putnam, it is entirely incoherent to suppose that you are a brain-in-a-vat since there is no reality that your words refer to in the brain-in-a-vat case (alongside other sceptical cases like being in a dream).

Putnam’s argument also has weaknesses, consider the second part of this argument – why must ‘tree’ always refer to real trees? Some might say that the brain-in-a-vat case does not capture all sceptical cases. Does this argument work against the evil demon where both reason and senses are held under suspicion?
But, at the end of the day, all arguments have parts we can doubt and question. The point is – if you believe scepticism is wrong and Putnam’s argument correct – to shore up his defences and take the argument in new directions.

Let us consider the things which people commonly think they understand most distinctly of all; that is, the bodies which we touch and see. I do not mean bodies in general—for general perceptions are apt to be somewhat more confused—but one particular body. Let us take, for example, this piece of wax. It has just been taken from the honeycomb; it has not yet quite lost the taste of the honey; it retains some of the scent of the flowers from which it was gathered; its colour, shape and size are plain to see; it is hard, cold and can be handled without difficulty; if you rap it with your knuckle it makes a sound. In short, it has everything which appears necessary to enable a body to be known as distinctly as possible. But even as I speak, I put the wax by the fire, and look: the residual taste is eliminated, the smell goes away, the colour changes, the shape is lost, the size increases; it becomes liquid and hot; you can hardly touch it, and if you strike it, it no longer makes a sound. But does the same wax remain? It must be admitted that it does; no one denies it, no one thinks otherwise. So, what was it in the wax that I understood with such distinctness? Evidently none of the features which I arrived at by means of the senses; for whatever came under taste, smell, sight, touch or hearing has now altered—yet the wax remains.

Descartes, Meditations, Ch. I