Fundamental Principles of Scientific Inquiry. 373 



infinite classes. Thus his theory, like Mr. Russell's, is not 

 a possible theory of knowledge, whatever its status as a 

 metaphysic may be. 



The doctrine of universal consent, as a criterion of 

 scientific truth, is open to a similar objection, though it 

 does not involve the use of infinite classes. It has been 

 made part of the basis of Dr. N. R. Campbell's recent book, 

 * Physics : The Elements,' in which it is stated that only 

 those processes, logical and experimental, are admissible in 

 physics, which are universally agreed to be valid. The 

 object of this principle is to place scientific knowledge on 

 an apparently more secure foundation than the individual 

 judgment, and thus to distinguish it from metaphysics and 

 mysticism. But Dr. Campbell would not suggest that no 

 process is acceptable" in physics until it has been submitted 

 to the whole of mankind. If that was necessary, there 

 would be no theory in physics and very little practice : 

 the persons who can understand even the proof that 

 (x + a)(x — a) —x 2 — a 2 do not compose a tenth of mankind. 

 Some criterion is necessary to decide whose judgments 

 shall be omitted ; and this criterion, for obvious reasons, 

 cannot be a universal judgment. Also, supposing that 

 it had been decided that some classes of judgments were 

 admissible, in any new instance it would be necessary to 

 decide wh ther the new judgment was in fact a member 

 of that class or not, and this would consitute an individual 

 judgment. Thus universal consent is not an applicable 

 criterion in any case; it can, at the best, only be made 

 use of by means of inference. It is evident that the theory 

 of scientific knowledge should be based directly on the 

 more fundamental beliefs on which this inference is based, 

 and not on the universal consent itself. 



There seems to be .no possible foundation for science 

 intermediate between universal consent on the one hand 

 and the individual judgment on the other, for two reasons. 

 First, as in the case of the universal judgment, it would be 

 necessary in every instance to decide that the judgment 

 considered is a member of the class admitted by the 

 criterion, which is an individual judgment. Second, any 

 use of another person's judgments is based only on what he 

 has communicated to us ; and we can make no use of his 

 statements until we have decided both what they mean 

 and whether they are reliable, both of which, again, are 

 individual judgments. Thus we can make no use of the 

 judgments of others in our theory until the difficult 

 questions of the nature of language and the acceptability 



