Can we trust our senses in terms of their furnishing us with knowledge of the world?

We perceive our world through our senses. They are our input devices, our means of gathering information about the world we live in. They provide us with perceptual experiences. In attempting to refute scepticism, Descartes, and much more recently Putnam, extensively investigated the extent to which our sense perception is trustworthy in terms of providing us with knowledge. In seeking unshakable foundations for knowledge and discarding beliefs which were open to question, they hoped to be able to build a structure of knowledge beyond sceptical doubt. In this essay, I shall argue that the sceptics’ position is in fact made stronger through such thought experiments and that, in fact, there is no escape from the ‘brain in the vat’. One need not consciously believe that one is a disembodied brain at the whim of a malicious scientist and her super-computer, but one is compelled to accept the possibility of such a scenario. This acceptance, I suggest, undermines the value of perceptual experiences and therefore our claims to knowledge. I shall briefly define what I mean by ‘knowledge’. I shall be considering some of the arguments traditionally put forward by philosophers suggesting that our senses are open to deception and cannot therefore be a reliable knowledge source. I shall look at arguments which posit that our perception does reflect reality and as such provides us with knowledge. I will show why it is that I believe these objections to be invalid.

There are, I think, three basic ways in which we utilise the word ‘know’ and I wish to be very clear about which of these this essay is about. Firstly, propositional knowledge is that knowledge which follows from a proposition. For example, I know that my son is four years old. This is knowledge based upon the true proposition that he was born four years ago, and is hence four years old as I write. So propositional knowledge is based upon a relationship between an individual – or a subject - and a true proposition. (I think it fair to establish that ‘knowledge’ based upon a false proposition – i.e. that my son is ten years old – is in fact not knowledge, but mistaken belief.) The second use of the word ‘know’ might be referred to as acquaintance knowledge – as in the case where we claim to know someone, as a friend or acquaintance. This type of knowledge implies, rather strongly, direct personal experience; I know my son: his character and his moods are an everyday familiarity. Other people might know that I have a son, that he is four years old, that he is French – but unless they have actually met him, they can only claim propositional knowledge of him. This distinction is an important one. The third usage of ‘know’ applies to skills and abilities – a ‘how-to’ knowledge. I know how to drive and to use my computer (mostly). The focus of this essay is on the first of these uses of the word ‘know’ – propositional knowledge.

Propositional knowledge requires that the proposition (p) be true. This is rather self evident. Rather less self-evident, but vitally important, is the second requirement of propositional knowledge, that one believes p to be true. For me to claim that I have knowledge about something it must both be true and I must believe it to be so. There are many instances where a proposition is true, but I might not believe it to be so – in which case I cannot claim to have knowledge of it. Similarly, I might not believe a proposition, whilst it is in fact true. Other possibilities, such as claiming that something is true but at the same time claiming not to believe it, would seem to be self –contradictory. There is, though, a third requirement here. It might be possible for proposition to be true (for example that there is intelligent extraterrestrial life) and I may believe it to be true. However, until I know it to be true, I cannot claim this as knowledge. When we are visited by such life-forms, my belief will be justified, and then I shall have the grounds for knowledge. Before such a momentous visitation, I simply have an opinion, even if a strongly held one, which just happens to be true. Knowledge, therefore, for the purposes of the following discussion, can be summarised as justified, true belief.

Descartes was looking to answer the question, ‘did a reliable method exist, at least in principal, for getting knowledge and accumulating knowledge?’ He was looking for propositional knowledge of which he could be certain. So he sought to reject all experience that was open to question. ‘All that up to the present time I have accepted as most true and certain I have learned either from the senses or through the senses; but it is sometimes proved to me that these senses are deceptive, and it is wiser not to trust entirely to any thing by which we have once been deceived.’ He put forward a scenario where he is being deliberately and continuously deceived by an evil demon, and where nothing his senses have led him to believe can be considered true. In doing so, he found himself at his famous ‘cogito ergo sum’ which is probably best translated as ‘I am consciously aware, therefore I know I must exist.’ Whatever the demon is doing to me, I am still aware of me. To escape the seeming fact that this was all he could be sure of, Descartes resorted to what is at best a dubious proof of the existence of a benevolent God in order to permit that our senses are not being deceived by the ‘malin génie’. It is hard to see that Descartes escaped his own conundrum. He appears, conversely, to have provided fuel for the sceptics – in this case Idealists – in rather soundly removing sense perception as a means to knowledge.

Descartes’ idea was not original to him. To some extent, it can be traced back to Plato’s Allegory of the Cave. There, shackled prisoners experienced a watered-down version of reality (the shadows cast on the wall of a cave by puppeteers using a fire as a light source) which they took to be real. Such was the extent of their deception, that an escaped prisoner returning to them, having seen for herself the truth (symbolised nicely by the sun outside the cave) is ridiculed, even threatened. We tend to resist the notion that our senses are mistaken, or being deceived. This is powerfully demonstrated in the film ‘The Matrix’, a modern extension of Putnam’s ‘brain in a vat’ re-positing of Descartes’ evil demon. In the film, Neo is ‘freed’ from the Matrix, much as is the prisoner in Plato’s cave. Morpheus explains to him, ‘It [the Matrix] is the world that has been pulled over your eyes, to blind you to the truth...that you are a slave, Neo. Like everyone else, you were born into bondage, born into a prison that you cannot smell or taste or touch. A prison for your mind.’ When Neo hears this he is physically sick, he rejects the idea and his first impulse is to return to the Matrix. (This is a feat successfully accomplished later in the film by another character, Cypher, who concludes that ‘ignorance is bliss’ when he makes a deal to be re-inserted into the Matrix, opting for simulated sensory experience over reality, with the proviso he remembers nothing.)

The power of Descartes’ demon, magnificently dramatised in ‘The Matrix’, is not that one is expected to genuinely believe that one is in fact a human battery, a disembodied brain or even shackled prisoner in a cave. A person exhibiting this belief in day to day life would be considered paranoid at the very least. The power is in the word ‘possibility’. That ‘The Matrix Possibility’ exists is enough to rock our knowledge foundations. I have to admit that I might be in the Matrix. This is unavoidable and hence things which I currently claim to know cannot be true. I have no way of knowing, through perception, reason or emotion, that I am not, in fact, currently in a pod of pink goo.

An obvious objection to this line of reasoning is that in the real world, we tend to think more of probability than of possibility. Whilst the Matrix is possible, it is intuitively highly improbable. Outside of philosophical papers, probable is more important. Show me that my idea is possibly false and I will seek to defend it, show me that it is probably false and I ought really to re-think it. On the improbability of the Matrix, one could look, however, to the work of Nick Bostrom. He suggests that it is highly likely that civilisation reaches a point where technology can simulate human minds effectively. Once this happens, the experiences of biological minds and computerised minds will be identical and both will think themselves not simulated. Simulated minds will far outnumber biological ones, since the technological capacity for storage is increasing so rapidly. We posit this in terms of a futuristic world, but cannot be sure that this future world has not already happened. Maybe it has, and we are simulated minds, programmed, of course, to think that we are not. The logic appears sound. And the Matrix thus becomes probable, not just possible.

Other objections exist. The idea that the world is just as it appears to us is often called naive realism. (One would be excused for inferring, from popular usage of the word, that this means that if one considers that one is actually sitting at a desk, tapping grey keys on an Acer laptop, listening to the English Chamber Orchestra’s rendition of ‘Silent Night’, one simply hasn’t really thought about it. Common-sense realism might be a better term.) Basically, four beliefs prevail. Firstly, there is an external physical world. Secondly, through our senses we can know propositions about it to be true: the sky is blue, fire is hot. Thirdly, these things are permanent – they don’t disappear when I do not perceive them (the tree in my garden is still there when I close my curtains). Finally, and crucially, we perceive the world much as it is and our claims to knowledge about it are, on the whole, justified and true.

One common objection to realism is that we cannot know things as they really are, only as they seem to us. If our eyes were differently constructed, fewer rods and more cones for example, or we used sonar instead of light vision, our perception of the world would be unimaginably different. All of our senses could be differently constructed, and hence our world view would be different. Illusions provide another fertile ground for objecting to realism. The stick half immersed in water is in fact straight, though it appears to me to be bent. The physical pain felt in an amputated limb also questions the validity of our senses.

Can a simple instance show that our senses can deliver knowledge? If I see an apple, ripe and red, do I not know it is an apple? I think that clearly if I have never had experience of apples, then I could not claim to know this. Could I at least claim to know that it was fruit, or food, or just red? Equally, I would suggest, without the previous experience of these concepts, our senses merely show us a scene – one which could be unintelligible and meaningless. Only when we apply understanding, use reason and appeal to previous experience can we begin to have knowledge. Kant wrote, in Critique of Pure Reason, ‘All our knowledge begins with the senses, proceeds then to the understanding and ends with reason.’ Kant proposed that there must be a mind-independent world existing outside of our sense experience since we can only make sense of perceptual experiences as responses to an external world. Hence, our senses give us the certain knowledge of the existence of an outside world. Kant’s transcendental idealism was a development of Berkeley’s idealism, that there is no external world independent of our experience of it. ‘To be is to be perceived,’ Berkeley wrote. This, however, begs the age-old question, ‘If a tree falls in the forest and nobody is there to hear it, does it make a sound?’ Berkeley was aware of this but his solution, to my mind, is no solution. He posits an omnipresent God, observing everything all the time, on our behalf. In other words, whilst Berkeley suggests that the world outside of our experiencing it doesn’t exist, it at the same time does exist, because God experiences it. I think that proposing something even more incredible as a means of explaining something incredible is intrinsically flawed.

The problem of the external world – do I have knowledge of how the world is, or only of how the world appears to be? – seems immutable. From the fact that there are dreams, hallucinations, perceptual errors and illusions, it seems clear that sensory experiences cannot present the actuality of the outside world. At best, they convey how it appears to us. The very possibility of The Matrix – that in some way we are being deceived and manipulated – is enough to make us doubt all. Much in the same way as Plato’s prisoner goes through a painful and gradual correction to the world outside the cave, ‘Neo’s rehab [in The Matrix] is painful. “Why do my eyes hurt? Neo asks. “Because you’ve never used them,” Morpheus replies.’ In a very real sense, none of us has. There is no escape from the ‘brain in the vat’.

 

Bibliography
Descartes – ‘Key Philosophical Writings’ (Translated: Haldane and Ross, edited: Chavez-Arvizo) Wordsworth Editions Limited, 1997
Dupré, Ben, ’50 Philosophy Ideas you really need to know’ Quercus Publishing, 2007
Hospers, John – ‘An Introduction to Philosophical Analysis’
Routledge and Kegan Paul, Second Edition 1985
Irwin, William (ed) – ‘The Matrix and Philosophy: Welcome to the desert of the real’
HarperCollins Publishers, Inc. 2002
Lemos, Noah – ‘An Introduction to the theory of Knowledge’
Cambridge University Press, 2007
Pritchard, Duncan – ‘What is this thing called Knowledge?’ Routledge, 2006
Warburton Nigel (ed) - ‘Philosophy- Basic Readings’ Routledge, 2005