212 SCIENTIFIC METHOD IN PHILOSOPHY 



But besides the logical analysis of the common 

 knowledge which forms our data, there is the considera- 

 tion of its degree of certainty. When we have arrived 

 at its premisses, we may find that some of them seem 

 open to doubt, and we may find further that this doubt 

 extends to those of our original data which depend upon 

 these doubtful premisses. In our third lecture, for 

 example, we saw that the part of physics which depends 

 upon testimony, and thus upon the existence of other 

 minds than our own, does not seem so certain as the 

 part which depends exclusively upon our own sense-data 

 and the laws of logic. Similarly, it used to be felt that 

 the parts of geometry which depend upon the axiom of 

 parallels have less certainty than the parts which are 

 independent of this premiss. We may say, generally, 

 that what commonly passes as knowledge is not all 

 equally certain, and that, when analysis into premisses has 

 been effected, the degree of certainty of any consequence 

 of the premisses will depend upon that of the most 

 doubtful premiss employed in proving this consequence. 

 Thus analysis into premisses serves not only a logical 

 purpose, but also the purpose of facilitating an estimate 

 as to the degree of certainty to be attached to this or 

 that derivative belief. In view of the fallibility of all 

 human beliefs, this service seems at least as important 

 as the purely logical services rendered by philosophical 

 analysis. 



In the present lecture, I wish to apply the analytic 

 method to the notion of " cause," and to illustrate the 

 discussion by applying it to the problem of free will. 

 For this purpose I shall inquire : I., what is meant by 

 a causal law ; II., what is the evidence that causal laws 

 have held hitherto ; III., what is the evidence that they 

 will continue to hold in the future ; IV., how the 



