The first generation of verificationists sought to eliminate metaphysics wholesale by a single application of a single criterion. The second generation recognized that the verificationist attitude could not be summed up in a single formula. The verification principle collapsed as soon as it was stated. Yet the attitude might still be applied to individual problems. Each problem, it could be agreed, had its own pathology, but most would yield to a deft and individual verificationist treatment. Some of the problems were new, engendered by a new science or technology, but others were old. Few problems of epistemology are more ancient than the sceptical doubt we examine in this chapter, ‘Is it possible that with all the experiences before me as I seem to write these words, I am in fact dreaming?’ Plato presents it with his customary elegance: