"WHAT IS MR. X?" 269 



which respond to my volition) extend the data, i.e. I can 

 perform experiments on X. For example I can make 

 a chemical analysis. The immediate result of these 

 experiments is the occurrence of certain visual or 

 olfactory sensations in my consciousness. Clearly it is 

 a long stride from these sensations to any rational in- 

 ference about Mr. X. For example, I learn that Mr. X 

 has carbon in his brain, but the immediate knowledge 

 was of something (not carbon) in my own mind. The 

 reason why I, on becoming aware of something in my 

 mind, can proceed to assert knowledge of something 

 elsewhere, is because there is a systematic scheme of 

 inference which can be traced from the one item of 

 knowledge to the other. Leaving aside instinctive or 

 commonsense inference — the crude precursor of scien- 

 tific inference — the inference follows a linkage, which 

 can only be described symbolically, extending from the 

 point in the symbolic world where I locate myself to the 

 point where I locate Mr. X. 



One feature of this inference is that I never discover 

 what carbon really is. It remains a symbol. There is 

 carbon in my own brain-mind; but the self-knowledge 

 of my mind does not reveal this to me. I can only know 

 that the symbol for carbon must be placed there by 

 following a route of inference through the external 

 world similar to that used in discovering it in Mr. X; and 

 however closely associated this carbon may be with my 

 thinking powers, it is as a symbol divorced from any 

 thinking capacity that I learn of its existence. Carbon 

 is a symbol definable only in terms of the other symbols 

 belonging to the cyclic scheme of physics. What I have 

 discovered is that, in order that the symbols describing 

 the physical world may conform to the mathematical 

 formulae which they are designed to obey, it is necessary 



