no SCIENTIFIC METHOD IN PHILOSOPHY 



where they go beyond sense-data, are at no point in 

 contradiction with sense-data, but, on the contrary, are 

 ideally such as to render all sense-data calculable from a 

 sufficient collection of data all belonging to a given 

 period of time. Now physics has found it empirically 

 possible to collect sense-data into series, each series being 

 regarded as belonging to one " thing," and behaving, 

 with regard to the laws of physics, in a way in which 

 series not belonging to one thing would in general not 

 behave. If it is to be unambiguous whether two 

 appearances belong to the same thing or not, there must 

 be only one way of grouping appearances so that the 

 resulting things obey the laws of physics. It would be 

 very difficult to prove that this is the case, but for our 

 present purposes we may let this point pass, and assume 

 that there is only one way. We must include in our 

 definition of a "thing" those of its aspects, if any, which 

 are not observed. Thus we may lay down the following 

 definition : Things are those series of aspects which obey the 

 laws of physics. That such series exist is an empirical 

 fact, which constitutes the verifiability of physics. 



It may still be objected that the " matter " of physics is 

 something other than series of sense-data. Sense-data, 

 it may be said, belong to psychology and are, at any 

 rate in some sense, subjective, whereas physics is quite 

 independent of psychological considerations, and does not 

 assume that its matter only exists when it is perceived. 



To this objection there are two answers, both of some 

 importance. 



(a) We have been considering, in the above account, 

 the question of the verifiability of physics. Now verifi- 

 ability is by no means the same thing as truth ; it is, in 

 fact, something far more subjective and psychological. 

 For a proposition to be verifiable, it is not enough that 



