Peter Medawar

Today the world changes so quickly that in growing up we take leave not just of youth but of the world we were young in.

The bells which toll for mankind are most of them anyway like the bells of Alpine cattle they are attached to our own necks and it must be our fault if they do not make a cheerful and harmonious sound.

I cannot give any scientist of any age better advice than this: the intensity of a conviction that a hypothesis is true has no bearing over whether it is true or not.

Scientific reasoning is a kind of dialogue between the possible and the actual, between what might be and what is in fact the case.