Philosophers and psychologists share a taste for the bizarre. Philo sophers have been known to speculate about brain transplants, the destruction and reconstruction of a human being and even the existence of a twin earth, complete with the twin of every living creature on the planet we inhabit. By comparison, the curiosities one can encounter in psychological textbooks and journals seem small fry. Nevertheless, there is an analogy between the purposes served by philosophical and psychological studies of this sort, for in both cases the oddity is supposed to show something about the norm, whether this is the normal behaviour of a concept or the normal functioning of whatever processes underlie our possession and exercise of psychological capacities. This chapter will examine a psychological phenomenon which is sufficiently strange to have proved of interest both to psychologists and to philosophers. The phenomenon is known as ‘blindsight*.