THE EXTERNAL WORLD 65 



lecture, will be found to be more apparent than real, 

 and it will be shown that whatever there is reason to 

 believe in physics can probably be interpreted in terms 

 of sense. 



The instrument of discovery throughout is modern 

 logic, a very different science from the logic of the 

 text-books and also from the logic of idealism. Our 

 second lecture has given a short account of modern logic 

 and of its points of divergence from the various traditional 

 kinds of logic. 



In our last lecture, after a discussion^of causality and 

 free will, we shall try to reach a general account of the 

 logical-analytic method of scientific philosophy, and a 

 tentative estimate of the hopes of philosophical progress 

 which it allows us to entertain. 



In this lecture, I wish to apply the logical-analytic 

 method to one of the oldest problems of philosophy, 

 namely, the problem of our knowledge of the external 

 world. What I have to say on this problem does not 

 amount to an answer of a definite and dogmatic kind ; 

 it amounts only to an analysis and statement of the 

 questions involved, with an indication of the directions 

 in which evidence may be sought. But although not 

 yet a definite solution, what can be said at present seems 

 to me to throw a completely new light on the problem, 

 and to be indispensable, not only in seeking the answer, 

 but also in the preliminary question as to what parts of 

 our problem may possibly have an ascertainable answer. 



In every philosophical problem, our investigation 

 starts from what may be called " data," by which I 

 mean matters of common knowledge, vague, complex, 

 inexact, as common knowledge always is, but yet some- 

 how commanding our assent as on the whole and in some 

 interpretation pretty certainly true. In the case of our 



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