Some of these articles were written more than a quarter of a century ago, when I was teaching philosophy in Oxford; when Dr Henry Hardy proposed to me that they should be included in a separate volume, I demurred. Although I do not think that there is anything in them that I should now wish to withdraw or change radically (I could not bring myself to re-read them), it seemed to me that they belonged too much to their time and place - they were not untypical of the kind of discussions and controversies, mainly about positivism, that went on in Oxford in the years immediately before and after the war, but I thought that they contained little or nothing worth resuscitating nearly thirty years later. I felt similar doubts about the articles written in the years that followed. Dr Hardy thought better of these pieces than I did, and when I continued to be obdurate, he proposed that we should go to arbitration and suggested that Professor Bernard Williams be appealed to. Bernard Williams is an original philosopher and a just and candid critic, and I therefore expected him to agree with me. When he said that he favoured republication, I could not, of course, help being pleased, and I accepted his verdict even though I wondered whether it was not more generous than just. Dr Hardy pressed his advantage and persuaded Professor Williams to back his judgement by writing an introduction to the volume. For this act of what I can only describe as heroic friendship I record my deep gratitude.