372 INTRODUCTION TO PHILOSOPHY OF SCIENCE 



Yet one should note that a cause which is both sufficient 

 and necessary does depend upon its effect in the sense that 

 from the existence of the effect one could infer both the fact 

 and the degree of the cause. It must be admitted, therefore, 

 that a causal law is reversible in the sense that from the 

 cause one can infer the effect and from the effect one can 

 infer the cause. As a consequence, if one admits that con- 

 comitant variation characterizes the causal correlation defini- 

 tively, he finds it hard to deny the legitimacy of reducing the 

 causal law to a functional relation. 



But this is just what many would deny. For in eliminating 

 from causal correlations everything but concomitant varia- 

 tion, they would insist, one is rejecting precisely that feature 

 which is essential, and which was described a moment ago as 

 "causal efficacy' and "temporal asymmetry." In other 

 words, there is a peculiar asymmetry in the relation of cause 

 and effect; in the general correlational sense cause may be 

 inferred from effect, and effect may be inferred from cause. 

 But because of this uniquely asymmetrical feature effect 

 depends upon cause in a way in which cause does not de- 

 pend upon effect. It thus appears that nature exhibits in 

 still another form a factor which vitiates the reduction of 

 causal connection to functional relation. Causal laws can 

 be expressed as functional laws only if one neglects the fact of 

 causal efficacy, or temporal asymmetry, or one-way dependence. 

 It may be that this unique and elusive feature cannot be 

 described or located at all. But if it can, the reduction of 

 causal laws to functional relations can be accomplished only 

 by neglecting it. 



Can this unique feature be neglected? Certainly it can 

 upon grounds of method. Science is admittedly abstract; it 

 employs the principle of isolation and ignores those features 

 of the given which are presumed to be irrelevant. If the 

 scientist considers the asymmetry of the causal relation to 

 be unimportant, one cannot object if he chooses to exclude 

 it in the formulation of descriptive laws — provided one recog- 

 nizes that the resulting laws are abstract. As was suggested 



