"Nature, as well as human affairs, seems to be subject to both necessity and accident. Yet even accident is not completely arbitrary, for there are laws of chance, formulated in the mathematical theory of probability, nor can the cause-effect relation be used for predicting the future with certainty, as this would require a complete knowledge of the relevant circumstances, present, past, or both together, which is not available. There seems to be a hopeless tangle of ideas. ...if you look through the literature ...you will find no satisfactory solution, no general agreement. Only in physics has a systematic attempt been made to use the notions of cause and chance in a way free from contradictions. Physicists form their notions through the interpretation of experiments. This method may rightly be called Natural Philosophy, a word still used for physics at the Scottish universities. ...My material will be taken mainly from physics, but I shall try to regard it with the attitude of the philosopher... I know that such an attempt will not find favour with some philosophers, who maintain that science teaches only a narrow aspect of the world, and one which is of no great importance to man's mind. It is true that many scientists are not philosophically minded and have hitherto shown much skill and ingenuity but little wisdom. ...Wise men would have considered the consequences of their activities before starting on them ; scientists have failed to do so, and only recently have they become conscious of their responsibilities to society. They have gained prestige as men of action, but they have lost credit as philosophers. Yet history shows that science has played a leading part in the development of human thought. It has not only supplied raw material to philosophy by gathering facts, but also evolved the fundamental concepts on how to deal with them. It suffices to mention the Copernican system of the universe, and the Newtonian dynamics which sprang from it. These originated the conceptions of space, time, matter, force, and motion for a long time to come, and had a mighty influence on many philosophical systems. It has been said that the metaphysics of any period is the offspring of the physics of the preceding period. ...more than 200 years after Newton there should be some progress in the assimilation of mathematics by those who are interested in natural philosophy. So I shall use ordinary language and formulae in a suitable mixture; but I shall not give proofs of theorems (they are collected in the Appendix)."