82 THE SCIENCE OF LOGIC 



result of the change (the effect &quot;in facto esse&quot;} on the other. 

 They rightly distinguished in every such process the (material) 

 substances or agents at work (substantial causes), the forces or 

 powers (proximate principles of action) through which those 

 agents or causes act, and the action or process of change itself 

 (218). They distinguished, furthermore, between the extrinsic 

 causes (efficient andjinaf), which they called &quot; causes of the actual 

 change&quot; (i.e. of the &quot;fieri&quot; ex production of the effect), and the 

 intrinsic causes (formal and material] which they called (con 

 stitutive) causes of the produced result or effect, in its completed 

 state (&quot; in facto esse &quot;.) * 



Ignoring those distinctions, modern writers have fallen into the error of 

 actually identifying the &quot; efficient cause &quot; with its &quot; effect,&quot; by regarding 

 each as a mere aspect of the process of change itself, and this latter, ap 

 parently, as the sole reality. For example, Professor Welton 2 arrives at this 

 conclusion : &quot; Cause and effect are not two but one. That they are in 

 separable is indeed recognized by the relativity of the very terms themselves. 

 A cause without an effect or an effect without a cause is a contradiction in 

 terms and unthinkable. But we must go farther and say that in content they 

 are absolutely identical. It is only in form that they can be distinguished 

 and then we may speak of the one as determining and of the other as deter 

 mined. Thus the combination of hydrogen and oxygen in the quantitative 

 ratio of two to one determines that the effect shall be water, and the character 

 of that effect is determined by the character of the elements which are com 

 bined, but the combined elements and the water are one and the same 

 identical substance, and this substance is the content both of the cause and of 

 the effect.&quot; 



This is indeed going very far ; much too far. To identify the efficient 

 cause with its effect, the &quot;producer&quot; with the &quot;produced,&quot; is not only setting 

 popular thought and belief at defiance, but even espousing the implicit contra 

 diction that an effect can produce itself. 



When, therefore, we come to reflect on the immediateness of the cause to 

 the effect, we see that while the scientist must indeed aim at grasping the former 

 as closely as possible to the latter, in order to be sure of including every indis 

 pensable factor in the former, and so attaining as closely as he may to the ideal 

 of a reciprocal causal relation, he must guard equally against identifying the 

 cause with the effect, under pain of making all experimental search for &quot; causes &quot; 

 meaningless and impossible. For, if the effect is identical with the cause, then 

 when we know the effect we know the cause, and there can be no meaning in 

 searching for the latter. Our &quot; reciprocal relation &quot; appears to have become 

 a mere tautology ; &quot; The statement that cause and effect are identical . . . 

 becomes an extravagant paradox if taken seriously and applied to any particu 

 lar case of causation determined by scientific experiment &quot;. 3 



1 C/. ST. THOMAS, Summa Theol., i., q. 101, Art. i \-apud JOYCE, op. cit. t p. 

 248. 



*Op. cit. ii., p. 25. * MELLONB, op. ctt., p. 274. 



