The following discussion aims to show that our perception of the world is in no way illusory. Whilst we are obviously susceptible to illusions, our perceptual skills and cultural innovations enable us to recognise and exploit many of these these susceptibilities in a variety of powerful ways.
According to Alex Byrne: "Perception comprises, by stipulation, veridical perception and illusion" (2009). For Byrne, and many other philosophers, one “veridically perceives an object if and only if one sees it, and it is the way it appears or looks.” In other words, veridical perception is what we usually mean when we speak of perception in ordinary language. It is the perception of how objects ordinarily are, or what we typically call “ordinary perception”, “normal perception” or just plain “perception”. However, like Byrne, some philosophers claim that perception “comprises”, or at least sometimes involves, illusion or illusory perceptions. Two important points need to be made regarding this claim. Firstly, an illusory parrot is not a species of parrot—in fact it is not a parrot at all. And by the same token, an illusory perception is not a perception either, at least not in the respects in which it is illusory. The same is true of misperceptions, false perceptions or perceptual mistakes etc. A failure to perceive something in certain respects cannot be a sort of perception in those respects. Missing a train is not an instance of catching a train. Secondly, to perceive an illusion is not to fall under its spell. It is to recognise the illusion for what it is.
In a forthcoming book chapter, John O’Dea writes: "I can think of no good reason to deny that a tilted coin could be seen as elliptical and flat with respect to the viewer. This would be tantamount to denying the possibility of illusion." It is perfectly justified to say that a tilted circular coin can be treated, regarded or considered as a flatly presented ellipse, because a tilted circular coin can be successfully depicted as a flatly presented ellipse. However, if O’Dea intends “seen” in the sense of “perceived”, which seems likely in the context of his discussion, then his claim should be examined in light of the conclusions we have already drawn about the relation between perception and illusion. Thus, if the alleged perception is an illusion, then it is not a de facto perception in the relevant respects. On the other hand, if looking at a tilted circular coin results in a perception of an illusion—in seeing the illusion for what it is—then a description of the illusion alone will not answer the question of what has been perceived. What has been perceived is a tilted circular coin that can be successfully depicted through the use of a flatly presented ellipse.
In the concluding paragraph of the chapter, O’Dea writes:
Constancy often fails; deep shadows can make surface colour perceptually unclear; at severe angles, shapes constancy disappears; size becomes harder to judge from more distant objects; and so on. Is perceptual experience illusory in these conditions?
Evidently O’Dea confuses the illusion of inconstancy with actual constancy. Constancy is usually characterised as the stability we regularly encounter in the properties of perceived objects, despite changes in angle of view, illumination, shading etc. So if circumstances of apparent inconstancy do not constitute actual inconstancy, but rather the illusion of inconstancy, then it would be false to conclude that they are perceived as inconstant. A failure to see that a dead parrot is deceased is not a failure of constancy on the part of the parrot.
If the properties of a stable object, like a book or a table (or even a dead parrot), are perceived as having constancy, there is nothing to prevent us from also regarding, considering or treating these same objects as if they have inconstant features like being blurred when viewed at close quarters or being small when seen from a distance or being colourless in moonlight etc. This is important because it shows that we are often capable of treating things in two quite different ways, one of which involves the capacity to represent the actual properties we perceive whilst the other involves a more sophisticated knowledge of how to represent objects by way of illusory representational techniques.
The following passage from Maurice Merleau-Ponty makes a related point:
It took centuries of painting before the reflections upon the eye were seen, without which the painting remains lifeless and blind, as in the paintings by primitive peoples. The reflection is not seen for itself, since it was able to go unnoticed for so long, and yet it has its function in perception, since its mere absence is enough to remove the life and the expression from objects and from faces. [...] It is not itself seen, but makes the rest be seen. Reflections and lighting in photography are often poorly portrayed because they are transformed into things..." (2012, §364)
It is true that eyes quickly lose their lustre in the absence of lubrication, but if the reflection is not seen for itself, an obvious question arises. Is the reflection on a pond seen for itself, or the reflection in a mirror? Merleau-Ponty provides no obvious answer, but it seems reasonable to conclude that his view would be this. Until the discovery of depictive techniques capable of transforming reflections into things, people were not capable of representing them. In other words, it is by virtue of the emergence of pictorial techniques that visual phenomena like blurring, reflections, perspectival distortions etc. have become communicable (there is even evidence that this applies to the colour blue). This is not to say that reflections have not always played a part in perception. After all, if tears produced no reflections, they would be invisible. As Merleau Ponty says: the reflection “is not itself seen” but it enables the tears, the pond etc. to “be seen”. And what of mirrors? Do we not perceive the reflection in a mirror? His point is that the reflection is not perceived “for itself” as a thing. We might occasionally mistake a reflection for a thing, but this would not constitute a perception. It would be the perceptual equivalent of sitting on the platform of Glasgow Queen Street station dreaming that you are on the 8:15 to Edinburgh Waverly.
Schwitzgebel (2011) raises another reason to be wary about the claim that perception involves illusion.
Consider the oar's looking bent in water. Could we say that the oar's appearance is an illusion? That seems natural. But if so, then presumably the look of things through a glass of water, which will be similarly distorted, is also an illusion. And if that, then also the look of things through a magnifying glass held appropriately close? Through a telescope? Through ordinary corrective lenses? (166n.8)
It makes little sense to say, for example, that when things recede into the distance, they gradually become illusory. They are simply harder to make out. When we look across a table, we see less of the far side. This isn't an illusion. It's a commonplace and unremarkable consequence of the spatial fall-off of sensory input. The more distant an object, the less we see of it. The effect is regular and gradual and leads eventually to the complete loss of input as objects recede into the distance. If our sensory systems were perfect, there would be no fall-off. But then again, if our sensory systems were perfect, there would be nothing we could not perceive and there would be no such thing as partially seeing or barely hearing something etc. Partial perception and the gradual failure to make things out in certain respects are just normal characteristics of our sensory relation to the world.
In ordinary circumstances, when we perceive things normally, we often describe them as if they have properties that they do not actually possess. We might say that shiny surfaces commonly "look silvery or wet", that rainclouds "look leaden or grey" or that fast-moving objects "appear to be blurred". These are not perceptual claims, but they do not preclude other ways of representing things in terms of their actual perceived properties. In normal usage though, it doesn't really matter which strategy of representation we invoke in describing the objects we see, because we all share the same cultural tools and we are all subject to very much the same perceptual strengths and weaknesses.
Very much less theoretical attention has been paid to those perceptual failures that are the logical corollary of success. […] In the wake of each positive perceptual advance the reciprocal logic of discrimination failure opens up new prospects for influential representational substitution. (Brook 1997)
This is a vitally important observation with profound implications. To be under the spell of an illusion is to be incapable either of recognising it or exploiting it. It is simply to make a mistake. However, to recognise an illusion is not only to be capable of recognising and perhaps avoiding other similar illusions. It is to have an insight into how other similar illusions might be staged. While many creatures are capable of learning from their mistakes, only tool-users are capable of recognising and exploiting their mistakes in the form of illusionistic tokens.