THE DEFINITION OF REALITY 285 



theories about the world are neither true nor false but 

 merely convenient or inconvenient. A favourite phrase 

 is that the gauge of value of a scientific theory is that it 

 economises thought. Certainly a simple statement is 

 preferable to a circumlocutory one; and as regards any 

 current scientific theory, it is much easier to show that 

 it is convenient or that it economises thought than that 

 it is true. But whatever lower standards we may apply 

 in practice we need not give up our ideals; and so long 

 as there is a distinction between true and false theories 

 our aim must be to eliminate the false. For my part 

 I hold that the continual advance of science is not a 

 mere utilitarian progress; it is progress towards ever 

 purer truth. Only let it be understood that the truth 

 we seek in science is the truth about an external world 

 propounded as the theme of study, and is not bound up 

 with any opinion as to the status of that world — whether 

 or not it wears the halo of reality, whether or not it is 

 deserving of "loud cheers". 



Assuming that the symposium has been correctly 

 carried out, the external world and all that appears in it 

 are called real without further ado. When we (scientists) 

 assert of anything in the external world that it is real 

 and that it exists, we are expressing our belief that the 

 rules of the symposium have been correctly applied — 

 that it is not a false concept introduced by an error in 

 the process of synthesis, or a iiallucination belonging to 

 only one individual consciousness, or an incomplete 

 representation which embraces certain view-points but 

 conflicts with others. We refuse to contemplate the 

 awful contingency that the external world, after all our 

 care in arriving at it, might be disqualified by failing 

 to exist; because we have no idea what the supposed 

 qualification would consist in, nor in what way the 



