I should like, in the first place, to express my deep and humble appreciation of the honour of your invitation to me to deliver this year's Maudsley Lecture. I am very sensible indeed of the honour, and equally of the responsibility, which you have conferred upon me. In my attempt to carry out that responsibility I should be in total despair, were it not for one sentence in the letter of invitation which I received from your impeccable Secretary. He wrote ‘What we want is to listen to people in other fields talking on their own subject with sufficient of a bridge for some degree of mutual understanding.’ That modest hope seemed to me to be conceivably possible of fulfilment.