Towards the end of his paper on the unity of Popper's thought (Watkins, 1974: 403), John Watkins addresses the old problem of the irreconcilability of commonsense realism and scientific realism. "Realists", he says, "are faced with a painful choice: either cling to commonsense realism (grass really is green, etc.) and interpret science in some nonrealist way (for instance, instrumentally) or interpret science realistically and adopt a nonrealist view of experience (grass is not really green, we mentally "paint" it green"). … If we take science seriously, we must conclude that, although my perception of the orange is indeed caused by external realities, these are about as different as they could be from my idea of an orange — colourless, tasteless, very small. The orange exists only in my mind."