48 WHAT IS SCIENCE? 



said in further explanation and extension of this attitude ; 

 but space forbids a more lengthy discussion, and, with this 

 hint, the matter must be left. 



It may be noted that in the actual practice of science 

 none of these difficulties and complexities arise. Every 

 science starts, as has been said, from the crude and vague 

 laws which have been elaborated as the result of that 

 continuous tradition of experience which is called common 

 sense. And, just because they are so intimately part 

 of common sense, there is usually no difficulty whatsoever 

 in obtaining for them the universal agreement which 

 makes them the proper subject-matter of science. It is 

 only when science gets to work and, instituting a much 

 deeper and more thorough inquiry than common sense 

 would ever institute, finds that the relations asserted by 

 the laws are not strictly invariable, that the question 

 of doubting the laws arises ; and the very inquiry which 

 suggests the doubts suggests also how the laws may be 

 amended so that once more, for the time being, universal 

 assent for them may be obtained. It is not actually 

 difficult to get people to agree that there are such things 

 as air and water ; the actual difficulty is rather to make 

 them see that what they call air and water are really 

 many different substances, all differing slightly by small 

 distinctions which have been overlooked. When we 

 study the history and development of any actual science 

 and it must be remembered that this book is only 

 intended to be an introduction to such study we do not 

 find actually that difficulties are continually raised by a 

 failure to obtain universal agreement ; though at a later 

 stage it is easy to see that the supposed laws of an earlier 

 stage were not true laws and that agreement could not 

 have been obtained for them, at any one stage the 

 distinction between the laws which are assumed as funda- 

 mental and those which are based on them is perfectly 

 clear and definite. The criterion of universal agreement 



