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XLTI. On Certain Fundamental Principles of Scientific 

 Inquiry. By Dorothy Wrinch, D.Sc, Fellow of Girton 

 College, Cambridge, and Member of the Research Staff, 

 University College, London, and Harold Jeffreys, M.A., 

 D.Sc.y Fell oiv of St. John's College, Cambridge*. 



IN order that a scientific method may be of any value, 

 it must satisfy two conditions. In the first place, 

 it must be possible to apply it in the actual cases to which it 

 is meant to be relevant. In the second, its arguments must 

 be sound. The main object of science is to increase know- 

 ledge or the world, and if a method is not applicable to 

 anything in the world it obviously cannot lead to any 

 knowledge. This principle is very elementary, and it is 

 probably for that very reason that it is habitually overlooked 

 in theories of scientific knowledge. 



Any theory, whether scientific or purely logical, must rest 

 on a set of primitive propositions, called postulates. In 

 each case other propositions are deduced from these, one 

 by one, by a purely logical process. The difference between 

 pure logic and science lies in the nature of the primitive 

 propositions. In all cases these include the postulates of 

 pure logic ; but in scientific investigation they also include 

 two other kinds of proposition. The first of these consists 

 of the facts of sensory experience, which do not form a part 

 of logic; the second type are general propositions, involving 

 the non-logical concept of probability . This is necessary in 

 order to deal with the essential process of generalization, 

 and accordingly we think that any attempt to construct a 

 theory of scientific knowledge without it is foredoomed to 

 failure. The attempt has nevertheless been made several 

 times in different ways. In this paper we hope to indicate 

 the points at which these various attempts break down ; in 

 all cases it is found that they fail to satisfy the criterion 

 of applicability in practice. 



The second criterion is as necessary as the first, but it is 

 usually satisfied in scientific theories. Nevertheless, the true 

 nature of scientific argument is very imperfectly understood. 

 It is not difficult to suo-o-est a reason for this. The analvsis 

 of processes of reasoning has always been regarded by philo- 

 sophers as their special province, and they have habitually 



* Communicated by the Authors. 

 Phil. Mag. S. 6. Vol. 42. No. 249. Sept. 1921. 2 C 



