166 WHAT IS SCIENCE? 



intrude into such affairs it becomes as hesitating and 

 dubi table as any other source of knowledge. 



As a formal statement of the position, this objection 

 must be admitted as valid. The uniformly certain and 

 completely universal laws of science can be realized only 

 in the carefully guarded conditions of the laboratory, and 

 are never found in the busy world outside. There is 

 scarcely any event or process of practical importance to 

 which we could point as providing a direct confirmation 

 of any of the propositions of pure science, or which could 

 be described completely in terms of those propositions. 

 In every such event and process, there is involved some 

 element of which science can take no cognizance, and it 

 is usually on account of this element (as was remarked in 

 Chapter III) that the event has practical importance. 

 And again, it is the presence of this element which makes 

 it possible for experts, equally well-informed, to differ 

 in their preliminary suggestions of an explanation of the 

 event or of the most suitable means for controlling it. 

 But it does not follow because practical events do not 

 lie wholly within the realm of science that they lie wholly 

 without it. Indeed it is from the study of practically 

 important events that many of the results of pure science 

 have actually been derived. Let us examine the matter 

 more carefully. 



All the applications of science to practical life depend 

 ultimately on a knowledge of laws. Whether we are 

 asked to explain an event, or to suggest means whereby 

 an event may be produced or prevented, we can meet 

 the demand only if we know the laws of which the event 

 is the consequence. But laws state only relations between 

 events ; when we say that an event is the consequence 

 of certain laws, we do not mean that this event must 

 happen in all possible circumstances ; we mean only that 

 it is invariably associated with certain other events, 

 and must happen if they happen. The event in question 



