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The Physical World is a Fiction

Peter Lloyd casts a sceptical eye over… well, almost everything, really.

The proposition that appears in the title of this article may seem odd. And the reader will be entitled to demand, “What on Earth do you mean by this? Surely you can’t mean it literally?” Before getting on to this weird proposition, however, I need to prepare some ground. I must try to persuade you that the foundations are sound, before asking you to consider what is built on them. Therefore I shall illustrate the argument that I shall use to support this weird stuff, by applying it in an uncontentious case.

Illustration of the Argument

Consider the curious phenomenon of the Pinkel Triangle1. This is a triangle that has four sides, rather than the usual three. Of course, it has precisely three corners, else it would not be a triangle at all. Like the familiar three-side d triangle, it is classified by how many sides have the same length: the equilateral (all sides equal), isosceles (two sides equal – which can be neighbouring or opposing), tripodal (three sides equal), or irregular (all sides different).

You and I both know that the Pinkel Triangle is a fiction. But precisely how do you know? Well, one route to that conclusion is to infer that the triangle must be a fiction from the fact that nobody could ever come across a Pinkel triangle in the real world. You can never see a Pinkel Triangle; nor can you ever touch one or detect one with any instrument. There is no experimental procedure that anybody could ever carry out that could reveal the existence of a Pinkel Triangle. Moreover, it is not merely impossible to do so, it is inconceivable: the concept of finding a Pinkel Triangle is logically incoherent. Any claim to have perceived or detected a Pinkel Triangle is unintelligible; it is devoid of any substantive meaning. This is simply because it is selfcontradictory. If a planar shape has three corners, then it must inevitably have only three sides.

Of course, people can pretend to find Pinkel Triangles. There was a notorious scandal some years ago when a gang of thugs claimed they could tell that some people possessed Pinkel Triangles, and attacked them. All they were doing was using the Pinkel Triangle as an arbitrary label for a group of people against whom they were prejudiced. They spied on people and – when they spotted some habit of behaviour that fell into the set of deprecated actions – they deemed their victims to have Pinkel Triangles and assaulted them. But I digress.

Since there is no conceivable notion of detecting a Pinkel Triangle, there is no difference between a real Pinkel Triangle and its fictional counterpart. Suppose I were to put a Pinkel Triangle on the table in front of you. How could you tell whether this was a real one or an imaginary one? You couldn’t! Since you cannot perceive or detect either a Pinkel Triangle or an imaginary triangle, there simply is no difference between them. “Huh?” the reader might interject, “Surely there is one big difference – namely the fact that one is real and the other imaginary. The mere fact that you can’t see this difference, doesn’t mean there’s no difference.” Not so! What you are referring to is just a difference in their designation, not a difference in the triangles themselves. At the risk of losing the reader in digressions, let me give another example. I have three Biros on my left and three on my right. I shall designate the ordinals of these two sets of Biros as ‘left-hand three’ and ‘right-hand three’, respectively. Obviously there is no difference between a lefthand three and a right-hand three. There is only a difference in their designations. (It is a moot point whether we could express this in Dr. Borr-Hess’s tautology, “The number three is the number three.”2) Likewise, a real Pinkel Triangle and an imaginary one have different designations (one is called ‘real’, the other ‘imaginary’), but there is no difference between the triangles themselves.

Therefore, we can conclude that the Pinkel Triangle is itself a fiction. All Pinkel Triangles are imaginary.

“Yawn!”, grumbles the unreceptive reader, “This is the very stuff of ivory-tower sophistry. To go through an elaborate argument just to prove the non-existence of something, which common sense tells us can never exist anyway.” I beg the reader’s patience. What is of interest here is not the Pinkel Triangle itself, but the logic of the argument. In this particular example, common sense does indeed tell us that the conclusion is true, and it should also help us to see that the argument is valid. For subsequent reference, I shall propose it in this formal scheme. The format is that if the premise (1) is true then you can infer the first conclusion (2) and hence the final conclusion (3).

1 . It is intrinsically inconceivable that we can ever perform any experiment or observation to detect the presence of X.

2 . Therefore any X is indistinguishable from a fiction.

3 . Therefore any X is a fiction.

If you disagree with this scheme, then I must ask you for a counter-example, or a contrary proof.

Application of the Argument

Now, let this X be the entire physical universe and all physical things in it: all matter, energy, space, time, force, motion, and so on. The whole shooting match.

I put it to you that you cannot be sure that X is really there. Science fiction fans will find this bit easy, and I must beg indulgence of those whose reading habits are more Chekhov than Asimov. The starting point for the sci-fi fans is to imagine that your brain is floating in a glass vat. A lifesupport system pumps a supply of oxygen and glucose into the brain, and extracts waste matter from the blood supply. A dense bank of electrodes connects the brain to a massive electronic computer. Signals are transmitted into the brain to create the impression that the brain inhabits a body walking around a threedimensional world. And other signals, which emanate from the brain’s motor cortex, are picked up by the computer and used to simulate the movement of the virtual body in the virtual space. So far this is fairly mundane, but now we must move from science fiction to science fantasy. The next step is to imagine that you do not even have a brain: that you are just a disembodied stream of consciousness floating in nothingness. (Forgive me if this seems puerile. Philosophy is like this sometimes.)

Now you have the idea of the whole physical world (X) being a figment of your imagination. Here’s the crunch: How do you know this is not how things really are? How do you know that you are not really a consciousness floating in a vacuum? “Well, it’s not very likely, is it?”, the reader may reply in a harsh tone of voice. “The chances of this science-fantasy scenario being true must be vanishingly small.” (I shall leave aside the difficult question of how you could actually quantify the probability of something so fundamental.) All I want you to do is to accept the possibility, not the probability: to agree that it really is conceivable that you are just a stream of consciousness with no physical substrate. It doesn’t matter that you regard this possibility as so unlikely that you would never seriously consider that it might be true.

If – yes, I know it’s a big ‘if’ – but if you were a disembodied consciousness, then you would never know it. By hypothesis, all your perceptions and sensory data appear as if you inhabited a material body in a three-dimensional world. So there would be nothing in your observations to tell you that this was not so. Even if you had some strange experience that suggested that the material world was not there, you could not have any means of checking the validity of that experience. For instance, if you were to meet some ancient Tibetan bloke with a white beard and a saffron robe, who told you that the world is an illusion – how could you check that he had got it right? You couldn’t! Any checking you did would consist in acquiring observations, which may or may not derive from a putative physical world. You could have no ‘direct line’ to the physical world to see whether it was there.

If the reader is an admirer of Dr. Johnson, she may well say, “Hold it! Of course I can check that the world is really here. I can just reach out and touch it. If I stub my toe against the desk, then I shall feel its force. This would not happen were the world not there.” Alas, this is to ascribe to the faculty of touch an authority that it does not possess. You can dream tactile sensations (although you may not do it often), and dream the resistance offered by solid objects. (I once dreamt that I was climbing up some concrete steps. Had I stubbed my toe against them, I might well have got a Johnsonian confirmation of their solidity.) The fact that the world around you feels solid does not give you any definitive evidence that there is any substance to it beyond those perceptions of apparent solidity.

Moreover, it is not merely impossible to acquire empirical evidence of the physical world’s existence. It is inconceivable. Any observation will be based on a perception – either directly through your sense organs or indirectly through a measuring instrument, the use of which would rely on reading a dial or some such display. It is not intelligible to have an observation of the world that does not come to you through one or other of your senses.

We therefore now find ourselves at step (1) of the argument that was outlined above. Substituting “the physical world” for X, we have:

1a . It is intrinsically inconceivable that we can ever perform any experiment or observation to detect the presence of the physical world.

Having got that premise, we can jump to step (2a), which follows from it:

2a . Therefore any physical world is indistinguishable from a fiction.

And finally step (3a), which follows from the foregoing:

3 a . Therefore any physical world is a fiction.

Thus we arrive at the weird conclusion of the title: that the physical world that we think we inhabit is just a useful fiction. And we have obtained this surprising conclusion just using common sense, without any high-flown philosophical theory.

Surely This Is A Joke?

“Come off it!”, the peeved reader might exclaim, “You know as well as I do that the world is real. This guff about the world being fictional is just playing with words. You can’t seriously expect anyone to believe your argument!” No and no. No, it is not just playing with words: it is a valid argument which, I believe, brings us to a true conclusion. But no, I don’t expect anyone to believe it. The reader would have to be daft to accept so radical a rethink of her world-view on the flimsy basis of this sketchy article. My hope, rather, is that it might nudge some readers in the direction of seriously considering whether the conclusion might be true. One can accept such a conclusion only by seeing that it is true – not by merely following a line of argument.

It took me about five years, from starting to think about the mind-body problem, to arriving at the firm conclusion that the physical world is a fiction. At first, I thought – as you probably do – that ‘mental monism’ (as this theory is called) is stuff and nonsense. The trouble is that our belief in the physical world is deeply ingrained in us. It is second nature to think that we are in direct contact with tangible objects. But philosophy, if it can be defined at all, is the art of breaking habits of thought: the art of thinking the unthinkable. The academic debate about Cartesian scepticism (the notion that we can doubt the existence of the world) is perennially popular because it involves trying to break certain long-held habits of thought. But there is a significant difference between considering mental monism as an intellectual proposition, and embracing it as an evident truth. One often hears philosophers saying, “Well, yes, we all know that you cannot prove or disprove mental monism. But we all know that it is wrong. We all know that the world really exists. Only a lunatic would seriously believe otherwise.” And it is this last point that I now want to discuss: how to be a mental monist without being mad.

Mental Monism Is Not Solipsist

“But”, the long-suffering reader asks, “why do you bother trying to tell anyone about mental monism? According to your theory, nobody else exists except you. In effect, you’re just talking to yourself.” Not so. The theory says only that other people’s bodies do not exist. It says nothing about their minds. As far as the theory goes, other people’s minds may or may not exist.

Personally, I believe that they do exist: I should be surprised if the common-sense view that every human has a (real) mind were mistaken. But the reader insists: “Hypocrisy! You said that don’t believe in the material world because your contact with it is mediated by your senses, which you don’t trust for some reason. But your contact with other minds is at one further remove. You cannot see or touch another person’s mind, can you? You can merely infer the existence of other minds from people’s overt behaviour. Therefore, you should be even more sceptical of other minds than you are of the physical world.” Alas, the gentle reader has missed one crucial point. Although I myself have no direct contact with other minds, those minds themselves do, if they exist. For instance, you know that your own mind exists, because you have direct and indubitable experience of its contents. Each mind that exists can have an awareness of its own existence. Therefore such minds cannot be fictions. This is in marked contrast to the physical world, for nobody can ever have direct experience of it.

Solipsism, which is the theory that only I exist (or, from your point of view, that only you exist) may or may not be true. But it gains no support from mental monism.

Mental Monism Is Not Heartless

Not having fully registered the previous point, the reader may proceed to rail against the supposed heartlessness of mental monism: “So, this means that you don’t care if there’s an earthquake, or a train crash, or a war. All these things are just fictions, mere figments of the imagination, in your eyes”. Not at all. These disasters are significant in so far as they impinge upon people’s consciousness, causing pain, fear, and grief. Since mental monism casts no doubt on the existence of minds or their contents, it in no way belittles the significance of these disasters.

Mental Monists Cannot Walk Through Walls

Yes, I know the theory says that walls are fictional. But no, this does not mean that you can walk through them. The sensation of resistance that you get when you push against a wall is manifestly real. So is the sensation of pain if you run into one. Although the world is a dream, it is not under our control. Quite obviously, we cannot arbitrarily change the contents of our external perceptions. There is some force outside me that governs my external perceptions, that regulates and controls the ‘dream’ that is my life. And, in particular, it prevents me from ‘dreaming’ that I can walk through walls.

“Well that’s a cop-out isn’t it? You’re suddenly throwing in this massive assumption about a mysterious ‘force’ that somehow makes your dream look like a solid, material world. Wouldn’t it be easier just to accept that the reason you can’t walk through a wall is that there’s a bloody solid wall there? Ever heard of Occam’s Razor? Well, why don’t you use it to cut out all this claptrap about a mysterious ‘force’ and get back to the bog-standard idea that there’s a solid physical world out there, and that’s why your perceptions look the way they do.” Unfortunately, that option is not available. The argument that I presented earlier shows that the physical world does not exist. (Go back and check it if you don’t believe me.) Nevertheless, I cannot walk through walls. Ergo, there must be some ‘force’ stopping me from doing so. I’m sorry if it sounds mysterious, but I really don’t know anything about the ‘force’, except that it must be a mental force.

So What?

Finally, let’s look at a question that everyone asks when they get over the shock of finding that they cannot disprove mental monism. “What difference does it make? The laws of physics and all the principles of engineering are precisely the same, whether you believe the world ultimately is mental or physical. If you’re saying it makes no difference whether the physical world is real or imaginary, then shut up and leave us with our familiar belief in its reality.” Ah, but that’s not quite what I said. I did not say that it makes no difference at all. I said that it makes no difference to our external observations. Allow me to expand on this, to make things clear. If we are studying the behaviour of – say – metal girders under stress in a bridge, then it makes no difference whether the physical girder really exists in an absolute sense. We make certain observations (through our senses) of the size and shape of the girder, and of the tensile strength of its material in laboratory experiments, and we then predict what we will observe (through our senses) of the girder’s behaviour when employed in the bridge – hence predict whether we shall see the bridge fall down or not. It could all be a dream. But, if it is a dream in which the laws of physics are respected, then its being a dream is of no consequence.

If, however, we are studying the conscious mind and its relation to the brain, then we find ourselves in a different ball-game. I refer not to the ‘natural history’ of the mind, the hotch-potch of observations and empirical rules of thumb that comprise psychology. I’m talking hard science. By which I mean clearly defined terms that slot into explicit fundamental laws, and rigorously derived theories that are potentially refutable by fresh observations. There is, at present, no science of the mind. But it would be a good thing to have a science of the mind. Over the past three hundred years or so, since physical science was invented, we have found it immensely valuable in satisfying our urge to understand the physical world, and of unparalleled utility in controlling natural phenomena. We may reasonably suppose that a science of the mind would bring comparable benefits.

Alas, there is a major obstacle to overcome before we can build a mental science. In a previous article (Philosophy Now No.6), I argued that the conscious mind is not physical. (I shan’t repeat the argument here, but I hope that you will at least be sympathetic to the idea, even if you don’t immediately give it the thumbs up.) If true, this creates a nasty problem. For it is impossible to imagine any causal connection between a physical system (the brain) and one that is outside physics (the mind). Therefore, when we try to lay the foundations for a rigorous science of the mind on top of our knowledge of the physical world, we shall find that it cannot stand up. We are laying those foundations in an inappropriate place. I do not mean that neuroscience is unreliable. For, as a branch of hard science, it is as safe as houses. Rather, I mean that neuroscience provides no suitable surface on which to anchor a theory of the mind. There is no point of contact between the two spheres.

Even if you had the most thoroughly detailed and precisely validated equations describing the behaviour of electrochemical traffic in the brain, you could predict zilch about what goes on in a conscious experience. For terms that denote conscious sense-data are not defined in terms of physical constituents. They stand on their own. Therefore those terms will never appear in the equations. At best, you could hope to record ad hoc correlations: such as, when Mary Smith sees a particular green colour, the group of brain cells called X1 is active. Such correlations are inherently incapable of being extrapolated beyond the precise conditions in which they are observed. If Mary sees a blueish-green colour, rather than the pure green one, will X1 be active then? Or will it be X2 instead? You cannot tell, unless and until you do a further experiment and thereby ascertain which neurons are actually active. Without an underpinning theory, you can never predict the answer. We need a set of psycho-physical laws, whose terms denote mental phenomena: only then can we predict conscious experiences.

How do we get out of this corner? How are we to reach a vantage-point where we can discover the principles that govern mental phenomena?

To find a way out of this impasse, we must recognise that the physical world is ultimately a useful fiction and that the mental world is the primary reality. A science of the mind must therefore start from the premise that the mental world obeys laws of its own, which are not derivable from the laws of physics.

“But”, the reader may object, “even if we need to augment our understanding of the world to include the mind, why must this ‘mental science’ be wholly independent of physics? Why not simply a new branch of physics? If the mind really lies outside the scope of recognised physical laws, surely we could just add new laws to accommodate mental phenomena? If, as it seems, there is a systematic correlation between mental and neural events, surely we could deem that relationship to be a new fundamental law of physics?” Alas, such an approach is doomed to fail. Since the physical world is a fiction, it can exert no causal influence on any mental process. (Contrariwise, since physics is self-consistent, mental events can never appear as causal factors in a physical process.) A complete explanatory theory of the mind must therefore be selfcontained with regard to causation.

Ultimately, it must be possible to derive some rules that say which physical events are tied to which mental events, but those rules cannot form part of a framework of causal explanation.

This, then, is why mental monism matters – and why it is not just a sterile exercise in sophistry, as many think. It offers the only valid starting point for the road to a complete and rigorous science of the mind.

1 Named after the English mathematician, Haughay Pinkel, 1899-1986.
2 Foundations of Arithmetic, Tlön Publishing House, 1917.

© Peter Lloyd 1994

Peter Lloyd is a freelance computer programmer and, increasingly, a freelance writer.

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