Published online by Cambridge University Press: 03 November 2016
If, like David Copperfield, you are on the road to Dover, for the first time and with no one to guide you, and you come to a point where the road forks, then of all your mathematical knowledge, only the method of reductio ad absurdum can help you. For if you choose the wrong turning, and find yourself in Folkestone, you may be quite sure you ought to have taken the other road.
Lecture delivered to the General Meeting of the Mathematical Association, 10th April, 1947.