You’ve read one of your four complimentary articles for this month.

You can read four articles free per month. To have complete access to the thousands of philosophy articles on this site, please SUBSCRIBE!

Tallis in Wonderland

Print Print

Email Email

Email Discuss

Facebook Twitter Reddit Google+
StumbleUpon Pinterest Delicious Digg

Seeing & Believing

Raymond Tallis looks for the missing link between them.

Like many of the readers of this column (I guess), my first philosophical thoughts were provoked by questions about the nature of reality and its relationship to the way things appear to us in taken-for-granted everyday life. In my early teens, I was occasionally assailed by the queasy feeling that the phenomenal world – the world just as it appears to us to be – might be a highly structured hallucination: that I was dreaming what I otherwise thought I was experiencing. Although these traditional ‘Cartesian’ experiences were only momentary, they triggered an abiding interest in the philosophy of perception. Reading an excellent paper recently by San Francisco philosopher Kent Bach, ‘Searle against the world: how can experiences find their objects?’ (available at for example) seemed like homecoming. Bach’s article triggered the thoughts (most of them somewhat tangential to his arguments) in this month’s column.

Seeing & Philosophising

The philosophy of perception traditionally begins with what is usually called ‘The Argument from Illusion’, though it also encompasses hallucinations. We can have experiences of objects that are not there, or be presented with appearances – such as a stick apparently bent by being plunged in water – that prove on further investigation to have been deceptive. It seems that there is a disconnection between our perceptual experiences and the objects they purport to be experiences of.

This suspicion is reinforced by the fact that actual things, things that are really there, may have different appearances depending on how we are experiencing them. A demonstrably square table-top may look diamond-shaped from many angles; a circular coin may appear elliptical. This is not, of course, as worrying as some philosophers would like us to think. When I look at an object, I am aware not only of the object, but also that I am looking at it from a certain angle, at a certain distance, in a certain light. In other words, our sense experiences come with warnings: ‘You are not seeing object O, period, but object O from a certain angle, at a certain distance, in a certain light.’ Unlike Dougal in the TV programme Father Ted, we do not think that a person whose apparent size diminishes with distance is actually shrinking.

The various allowances we make for the different conditions under which objects are perceived, generating different appearances, are driven by an assumption of what psychologists call ‘object constancy’. This truly remarkable faculty requires a self-consciousness that incorporates in our sense experiences an awareness of the perspectives from which we perceive objects. We are conscious of the conditions under which we see things as well as being conscious of the things themselves: we are self-perceiving perceivers; which is just as well, since there could be no experience corresponding to seeing an object ‘in-itself’, from no particular angle, or distance, in no particular light.

So the diamond-shaped table and the elliptical penny are corrected for. And there is an additional source of checking. If seeing is tinged with doubt, touching may resolve uncertainty. Few headless horses, pink elephants, and bends in sticks plunged into water survive attempts to grasp them. At a more sober level, we can trace out the roundness of the penny with a pencil and confirm the squareness of the table by measuring its sides. It is, after all, ordinary everyday perception that exposes misperceptions for what they are: we realise we are deceived when we see the table as diamond-shaped because we have more reliable experiences that tell us that the table is in fact square.

Even so, some still believe – or claim to believe – that our proneness to illusions implies that there may be no connection between perceptions and the existence of their objects: all perceptions may be illusory or hallucinations. Thus, it is possible that what we think is out there has no relationship to any reality independent of our experiences, and our thoughts about them may be (as John McDowell has put it) a mere “frictionless spinning in a void.”

This worry is reinforced (for some) by the fact that it is possible to generate experiences by direct stimulation of relevant parts of the nervous system – an observation that underpins Hilary Putnam’s famous thought experiment in which a brain floating in a vat of nutrients could, by being stimulated in the appropriate way, imagine itself to be located and active in a world, although the latter is in fact created solely out of its neural activity. The Brain in a Vat thought experiment should not trouble us, however. After all, setting it up presupposes a non-illusory material object such as a brain, in a real material world. And we have even more solid grounds for rejecting the possibility that we are always deceived by our senses: namely, if illusion were universal, there would be no reality with which to contrast it. As Gilbert Ryle pointed out, “there can be false coins only where there are coins made of the proper materials by the proper authorities” (The Concept of Mind, 1949). Finally, if perception were systematically in error, and thus completely disconnected from the world in which the perceiver actually is, it is difficult to see how the perceiver, qua organism, could survive or, indeed, what use her perceptions would be. To say that the very ideas of survival, of usefulness, and of organisms, may be themselves based in illusion, only shows the unsustainable cost of maintaining the case for global illusion.

The Gap

Even so, illusions do reveal a gap between our perceptions and the objects that we perceive. Defining that gap has exercised many philosophers, but at the very least we can agree that there is no guarantee in the experiences themselves that they really are of the things they appear to be experiences of. The relationship between an experience and its object is contingent. The reasons for this go very deep indeed.

At the heart of perception is an ‘aboutness’ – a reference to an object that is by definition something more than that which is revealed by experiences. This glass in front of me is not exhausted by any number of visual or tactile experiences of it – yours, mine, or those of any sentient beings. This follows from the fact that an object is not reducible to its presence as its phenomenal appearance to a subject. To put this the other way round (as did the American philosopher Barry Stroud), our knowledge of objects is under-determined by our sense experiences. Some philosophers of a ‘phenomenalist’ persuasion conclude that material objects are ‘logical constructs’ out of experiences. This, however, would make it difficult to understand the role of the object in occasioning our experiences of it. If the object were built up out of our experiences, how could the experiences owe their origin to the object?

An argument, perhaps, for another day and another column. For the present we note that the mismatch between the contents and the objects of sense experiences – or even of the sum total of the experiences – opens up some interesting lines of thought.

A traditional way of characterising a true perception as opposed to an illusion is that the former is caused by its object. For example, if my perception of a glass is not to be an hallucination or an illusion, the perception should have been caused by the glass. This experience of the glass or, more generally, of object O, is truly a perception P of O only if O actually caused it. It is not sufficient that our experience should be exactly like the perception we would have if O had caused it. (Clearly, we cannot be expected to see this causal connection between true perceptions and their objects, otherwise we could not be deceived in the way that, from time to time, we are: there would be no possibility of illusions and hallucinations.) Given that the causal links between objects and perceivers are contingent and not necessary, it is not surprising that the content of a perception is independent of the object supposedly causing it, and that there is room for illusions and hallucinations.

Problems of Perception

The causal theory of perception, however, is beset with problems. For a start, it is misleading to think of an object – a standing, stable item – as a cause of an event such as a perception. It is events that cause events; so the putative cause of P cannot be O itself, but something happening to the object that sets in train a succession of events that finally impinge on the perceiving subject. In the case of vision, the most promising candidate is the incident light bouncing from O into the eyes of the person seeing it eventually causing activity in the visual cortex.

But the replacement of O with an event in O as the cause of perception makes perception even more problematic. Somehow, out of an Event (or events) in an Object (let us call it Eobject) causing an event (or events) in a subject (Esubject) there arises a perception P which is then of O. O, of course, is beyond or outside of Esubject: it is ‘out there’ with respect to the subject ‘over here’; but O also transcends Eobject, given that O is more than the events that befall it. So we have an odd situation: if P is truly of O, P has to be caused by O, and yet, at the same time, O is more than anything that could cause P; and P is also more than any Esubject that any Eobject could cause!

This is not grounds for suspecting that the experienced world is an illusion (for reasons we have already given); but it is a valid reason for being deeply puzzled by perception, particularly since (as already noted) experiences that have no basis in real objects may appear identical to those that are truly of the objects that they seem to be of: hallucinatory experiences can be qualitatively indistinguishable from true perceptions. There is no reason why a hallucination of O arising as a result of spontaneous activity in the visual pathways of my nervous system (say) should not have an identical content to a true experience of O occasioned by a causal interaction between O and my sensorium.

So we are driven to two conflicting conclusions. The first is that the criterion for a true perception P is that it is caused by events in its object O. There is, as it were, an audit trail leading back from P to O. The second is that O and P are not in a straightforward causal relationship. This is shown by the fact that P’s being about, its referring to, or being focussed on, O, points in an opposite direction to any causal chain leading from O to P. This is why William Alston’s aphorism “causality is no substitute for awareness” (‘Searle on Perception’, 1997) is so precisely to the point.

While we maintain the fundamental difference between perceptions and hallucinations, and feel that the difference must somehow involve the differences in the causal paths that lead up to them, there doesn’t seem anything in the properties of the material object itself, or of the perceiving subject, that would make the former sufficient to cause the perception in the latter. At any rate, material objects don’t seem to have the wherewithal to make their presence felt to a perceiving subject, and it is not at all clear what, if anything, in the perceiving subject would confer the ability on material objects to make their existence into presence. Perception, in short, is deeply mysterious.

I began my philosophising by brooding over the world of appearances and sense experiences. Fifty years on, this is still a place to which my philosophical thoughts repeatedly return.

© Prof. Raymond Tallis 2013

Raymond Tallis’s most recent books are Reflections of a Metaphysical Flaneur (Acumen), and (edited with Jacky Davis), NHS SOS: How the NHS Was Betrayed and How We Can Save It (One World).


This site uses cookies to recognize users and allow us to analyse site usage. By continuing to browse the site with cookies enabled in your browser, you consent to the use of cookies in accordance with our privacy policy.