294 CAUSATION 



side a new situation has arisen. It is a consequence of 

 the advent of the quantum theory that physics is no 

 longer pledged to a scheme of deterministic law. Deter- 

 minism has dropped out altogether in the latest for- 

 mulations of theoretical physics and it is at least open 

 to doubt whether it will ever be brought back. 



The foregoing paragraph is from the manuscript of 

 the original lecture delivered in Edinburgh. The attitude 

 of physics at that time was one of indifference to deter- 

 minism. If there existed a scheme of strictly causal law 

 at the base of phenomena the search for it was not at 

 present practical politics, and meanwhile another ideal 

 was being pursued. The fact that a causal basis had 

 been lost sight of in the new theories was fairly well 

 known; many regretted it, and held that its restoration 

 was imperative.* 



In rewriting this chapter a year later I have had to 

 mingle with this attitude of indifference an attitude 

 more definitely hostile to determinism which has arisen 

 from the acceptance of the Principle of Indeterminacy 

 (p. 220). There has been no time for more than a hur- 

 ried examination of the far-reaching consequences of this 

 principle; and I should have been reluctant to include 

 "stop-press" ideas were it not that they appear to clinch 

 the conception towards which the earlier developments 

 were leading. The future is a combination of the causal 

 influences of the past together with unpredictable ele- 

 ments — unpredictable not merely because it is im- 



* A few days after the course of lectures was completed, Einstein 

 wrote in his message on the Newton Centenary, "It is only in the quan- 

 tum theory that Newton's differential method becomes inadequate, and 

 indeed strict causality fails us. But the last word has not yet been said. 

 May the spirit of Newton's method give us the power to restore unison 

 between physical reality and the profoundest characteristic of Newton's 

 teaching — strict causality." (Nature, 1927, March 26, p. 467.) 



