According to Hume, the ideas of the imagination differ from perceptual impressions only in their degree of vivacity. In Mindsight , which is inspired by Sartre and Wittgenstein, Colin McGinn sets out to attack this outdated view, while maintaining that there are important similarities between seeing and seeing with the mind's eye. In so doing, however, he defends a number of equally questionable claims himself.
McGinn begins with the question, "How does the mental act of seeing differ from that of visualising something?" This is the first sign that something is going wrong, for seeing (unlike imagining) is neither mental nor an act. McGinn's own answer to his question is that images are fundamentally different from "percepts". It is not clear, however, what a percept actually is, let alone that such things exist.
Suppose that I am perceiving the Parthenon, whereas you are merely visualising it. As McGinn argues, what I perceive and what you visualise are one and the same thing (the Parthenon).
It is also clear that what you imagine is not to be identified with your image of the Parthenon. For unlike the Parthenon itself, your image of it is merely something you might form in your mind when you imagine it (although not necessarily whenever you do so for, contra McGinn, it is possible to imagine an object without visualising it).
Now, if an image is meant to be the thing we form in our minds whenever we imagine something, we might think that, by analogy, a percept is what we form in our mind whenever we perceive something. But this cannot be right, for to perceive the Parthenon is not to form anything in one's mind.
We might therefore be forgiven for thinking that a percept, if it is to be anything at all, must be nothing other than the thing perceived, in which case the answer to the question "how do images differ from percepts?" would simply be that the former are things we form in the mind and the latter are objects that exist outside it.
This is definitely not McGinn's view, for he writes that "images and percepts are alike in both being directed towards external objects". Thus we are left wondering what a percept is meant to be.
Another confusing claim is that you "cannot think about something you are not paying attention to". But if I am standing in Bloomsbury, in what sense could I possibly be paying attention to the Parthenon in Athens, no matter how hard I think about it? And when I am thinking about Sherlock Holmes, are we to say that I am paying attention to him?
What McGinn actually has in mind here is the thought that we cannot form an image of something without paying attention to that image. In his own words: "images are attention-dependent". But this is doubly mistaken; first, because we can think about something without imagining (let alone forming an image of) it, and second, because it makes no sense to pay attention to a mental image. After all, there is nothing that would count as not paying attention to it.
Finally, turning his attention to dreaming, McGinn argues that "dreams consist of images" and that we "believe what we dream". But it is a well-known fact that many people's dreams are not image-based.
Furthermore, if last night I dreamt that I was Napoleon, it does not follow that last night I believed I was Napoleon (for the duration of the dream).
McGinn argues that if I am dreaming that I am about to be attacked by a tiger, then "I simply believe, in the dream, that I am about to be attacked by a tiger". But suppose that I dream that I am about to be attacked by a tiger unawares, in this case it cannot be true that in the dream I believe that I am about to be attacked.
Over the past few decades, the topic of imagination has largely been neglected within the philosophy of mind, with favour being given to current "hot" topics such as consciousness, artificial intelligence and the emotions. McGinn's clear style and sharp wit will do much to give the topic of imagination the attention it deserves. Be that as it may, the book contains a number of misconceptions; not only about imagination, but also regarding perception, attention and dreaming.
Constantine Sandis is associate lecturer in philosophy, Open University.