Imagine a banana. What colour is it? Yellow, of course. Now try to form a picture of one that doesn't exist, that can't exist: a blue banana with red spots. Imagine that. How did you do? If you found it hard, perhaps you ought to know that Igor Aleksander has a machine which can do that easily. When he asks it (in words) to produce an image of 'banana' that is 'blue with red spots', the image swims on to the screen in seconds. The idea of such a conscious machine seems absurd and almost heretical, and its advocates are often accused of sensationalism, arrogance or philosophical ignorance. Part of the problem is that consciousness remains ill-defined: many people argue that it will always lie beyond the remit of science, in the realm of philosophical speculation. Igor Aleksander now attempts to unravel these arguments dispassionately for a general audience and provide a rigorous definition of consciousness.