In the seventeenth century, the English philosopher John Locke provided one of the first statements of what became an influential view of secondary qualities: colour, smell, taste, noise, etc. When you look at grass it appears green. However, grass is made up of atoms and these are colourless rather than green. But is the light reflected from these atoms is green? Not exactly – it’s not as if you see green waves of light snaking their way from the grass. The reflected light is invisible (if it wasn’t it would get in the way of what you are looking at!). Your brain interprets this light as green? Undoubtedly, but what does that mean? There is nothing going on in your brain that is green – grey and gooey maybe, but not green. The greenness of grass is a perfectly real property but seems to exist nowhere at all. That was Locke’s view of secondary properties in general. Nevertheless, we can say that the greenness of grass is, partly but crucially, a matter of what is going on in your brain.
In some recent work on vision, however, the emphasis runs the other way. Under certain conditions, we are blind to changes that occur in our visual field, even though these changes are significant and occur in full view. The most convincing explanation of this is that our visual representations give us only the general gist of what is going on: they are more like rough sketches than photographs. Of course, it doesn’t seem to us as if we see only the rough gist of what is going on. Our visual experience is rich, detailed and complex. So it is – but this stems from our ability to direct our attention at will to a world that is rich, detailed, and complex. If this is right, then properties we have attributed to our visual representations of the world – richness, complexity, and detail – are not to be found there at all.
One of the most tricky things about vision, it seems, is not working out what we see, or how we see it, but where we see it.
Mark Rowlands is author of The Philosopher and the Wolf (Granta)