If you see the drawing as such-and-such an animal, what I expect from you will be pretty different from what I expect when you merely know what it is meant to be. (L. Wittgenstein. Philosophical Investigations. 1953, p205e)
If you merely know that a child’s drawing is meant to be of a cat, it is probable that the drawing shares very little in common with a cat. But if someone mistook a photograph or skilful drawing of a cat for an actual cat, it would be extraordinary if the picture turned out to share nothing in common with a cat.
Now a simple phenomenological inspection of any representation, either a drawing or a photo, shows us that an image possesses none of the properties of the object represented. (U. Eco. “Critique of the Image,” 1970)
For Eco, the relation between images and “real phenomena” is “wholly arbitrary”. But this is surely mistaken. Words like “cat” have a wholly arbitrary relation to actual cats, but there is no question of our mistaking the word “cat” for a four-legged animal of the feline variety. If images share “none of the properties” of the things they represent, then how is it that we can sometimes mistake what turn out to be representations for the things they represent? Eco offers no explanation, but if it is true that we can sometimes mistake the properties of one thing for the wholly different properties of another thing, then it is reasonable to suppose that we must be dealing with some form of illusion.
It is important to realise here how familiarity, so to speak, takes the edge off illusion. Is the cinema a case of illusion? Well, just possibly the first man who ever saw moving pictures may have felt inclined to say that here was a case of illusion. But in fact it's pretty unlikely that even he, even momentarily, was actually taken in; and by now the whole thing is so ordinary a part of our lives that it never occurs to us even to raise the question. We might as well ask whether producing a photograph is producing an illusion—which would plainly be just silly. (J. L. Austin. “Sense and Sensibilia.” 1960, p26)
Silly as it might be to ask such a question, it certainly wouldn't be silly to suppose that we could use a photograph to construct an illusion. Nor would it be silly in certain circumstances to momentarily mistake a life-sized photograph of a person for an actual person. So whilst familiarity may take the edge off illusion, it doesn’t eliminate the possibility of illusion and nor does it diminish the importance of the concept.
“The application of the concept of an illusion in general presupposes a concept of being wrong in the sense that were we never wrong in what we perceive, were we never to make a false judgement about what we perceive, we should not have the concept of an illusion.” (D. W. Hamlyn. Sensation and Perception. 1961, p196)
A few years earlier, Hamlyn (no relation by the way) made some similar remarks on the same subject:
There is not necessarily anything about an illusion which tells us that it is one, for if there were it would not be appropriate to say that we were ever taken in. This is not to say that it is always right to say of someone who sees something wrongly that he is taken in; for he may see it in this way despite the fact that he knows the thing in question is not like this. But in order for it to be appropriate to talk of illusions it must sometimes be the case that people are deceived.” (D. W. Hamlyn. “The Visual Field and Perception. 1957, p112)
Now if this person “knows the thing in question is not like this” then he is not seeing it “wrongly” at all. He is seeing it as anyone else with the same perceptual faculties would see it. Moreover he sees that it is illusory in some respects and he probably also knows that other people would find it illusory in the same ways. So if I say that the moon looks like a proximate flat silvery circle, I am not making a perceptual claim that should be regarded as an instance of false or wrong perception. I am using a commonplace expression that will usually be readily accepted by anyone familiar with the ways in which illusory appearances are generally expressed in language.
Shared discriminatory capacities are a precondition for shared concepts of colour, taste, sound, smell, etc. Moreover, shared propensities for perceptual illusion are a precondition for shared concepts of perceptual appearances as distinct from actualities, viz. concepts of objects publicly looking thus-and-so although not being so. (Baker and Hacker. Wittgenstein: Rules, Grammar and Necessity. 2010, p.215)
One of my principal aims in exploring these issues is to show how these “concepts of perceptual appearances” are linguistic outgrowths from innovations in illusionistic representation. In other words, without these techniques, it would make no sense to say that yonder house looks small or that a glossy surface looks wet or that a static white cinema screen looks like a multi-coloured window onto a world of moving objects and people.
It may be that people without any experience of pictorial simulation would not say that the distant hills look blue, but even such innocents would probably be tricked, by being smuggled into a good planetarium, into believing that they were looking at the open night sky. (D. Brook. “How to Draw the Curtains.” 1985. My emphasis)