130 THE GRAMMAR OF SCIENCE 



particular order of the stages in the sequence as in the 

 result of experience that this order can exactly repeat 

 itself. 



The reader may perhaps wonder how, if the sequences 

 of sense-impressions are really of the chaotic nature re- 

 presented by our first series of numbers, it is possible to 

 describe such sequences apart from their repetition by 

 those brief formula; we term scientific laws. As the per- 

 ceptive faculty presents us, indeed, with the sequence, it 

 is undeniably more like the second than the first series of 

 numbers, for natural phenomena can without doubt be 

 largely described by certain brief laws. We must rather 

 put the actual case in the following form. We observe 

 a person whose motives are quite unknown to us writing 

 down the series — 



I, 2, 4, 8, i6, 32, 



and at present he has reached the number 32. A law 

 describing the series is obvious — each number is twice 

 the preceding one. With a great degree of probability 

 we infer that he will now write down 64, especially if we 

 have seen him write the series up to and beyond 32 

 before. But there is nothing of logical necessity about 

 his writing 64 after the preceding numbers. Those 

 numbers, when we know the law, suggest his doing so, but 

 do not enforce it. 



We are now in a position to scientifically define cause. 

 Whenever a sequence of perceptions D, E, F, G is invari- 

 ably preceded by the perception C, or the perceptions C, 

 D, E, F, G always occur in this order, that is, form a 

 routine of experience, C is said to be a cause of D, E, F, 

 G, which are then described as its effects. No phenomenon 

 or stage in a sequence has only one cause, all antecedent 

 stages are successive causes, and, as science has no reason 

 to infer a first cause, the succession of causes can be 

 carried back to the limit of existing knowledge, and 

 beyond that ad infinitum in the field of conceivable know- 

 ledge. When we scientifically state causes we are really 

 describing the successive stages of a routine of experience. 



