98 THE SCIENCE OF LOGIC 



hypothetical &quot;principle,&quot; or does it also involve the categorical 

 &quot;belief&quot;? The answer is that if the laws of physical nature are 

 anything more than statements of mere abstract possibilities ; 

 if they are taken to imply the actual existence and operation, 

 throughout space and time, of the agencies they refer to, then 

 the inductive process by which we reach them does undoubtedly 

 imply not only the hypothetical principle, but also the categorical 

 belief. And that physical laws are interpreted in this latter 

 sense, as informing us not about mere abstract possibilities, but 

 about concrete actualities, past, present, and future, there can be no 

 doubt. In reference to such a law, for example, as &quot; Heating (M~} 

 an iron bar (S) causes its elongation (P] &quot;. Dr. Mellone * says 

 that &quot; the connexion between M and P is independent of time 

 and place. We can reason backwards to unobserved cases in 

 the past, and dip into the future and be sure that P will always 

 be produced by M&quot;. 



But how sure can we be about this latter? No surer than 

 we can be that heat and iron (M and S} will continue to exist ; 

 for unless they continue to exist, the operation can never take 

 place. And what certitude have we that they will continue to 

 exist? The physical, hypothetical certitude which Dr. Mellone 

 describes as an &quot; overwhelming presumption &quot;. In fact, we can 

 not extend or apply a single physical law to a single future case 

 or to a single past or distant case for that matter, if it lies out 

 side our actual experience without assuming (a) that the causes 

 it refers to are &quot;necessary,&quot; &quot;natural,&quot; or &quot;non-free&quot; causes, 

 and (b] that they have acted, are acting, or will act, in the case 

 contemplated, without any obstacle or impediment from the inter 

 vention of other causes. 



Similarly, Father Joyce 2 seems to take the &quot;principle of 

 uniformity &quot; as embodying not merely the abstract judgment 

 that &quot;anon-free cause acts uniformly in similar circumstances,&quot; 

 but also the judgment that &quot; such causes do exist and act in the 

 universe,&quot; when he says that &quot; in that principle we have the 

 guarantee that our universal judgment will be verified in fact. 

 Our judgment that A as such is the cause of a, would help us 

 but little, unless we further knew that in the real order the same 

 cause does actually always produce the same effect.&quot; 



This being the sense in which Mill understood the principle, it 



1 op. cit., p. 265. *op. cit., p. 219. 



