616 LOGIC OF THE MORAL SCIENCES. 



particular cause will produce the desired effect, but 

 not ascertained all the negative conditions which are 

 necessary, that is, all the circumstances which, if 

 present, would prevent its production. If, in this im- 

 perfect state of the scientific theory, we attempt to 

 frame a rule of art, we perform that operation pre- 

 maturely. Whenever any counteracting cause, over- 

 looked by the theorem, takes place, the rule will be at 

 fault: we shall employ the mfeans and the end will 

 not follow. No arguing from or about the rule itself 

 will then help us through the difficulty: there is 

 nothing for it but to turn back and finish the scientific 

 process which should have preceded the formation of 

 the rule. We must reopen the investigation, to in- 

 quire into the remainder of the conditions upon which 

 the effect depends; and only after we have ascer- 

 tained the whole of these, are we prepared to trans- 

 form the completed law of the effect into a precept, in 

 which those circumstances or combinations of cir- 

 cumstances which the science exhibits as conditions, 

 are prescribed as means. 



It is true that, for the sake of convenience, rules 

 must be formed from something less than this ideally 

 perfect theory; in the first place, because the theory 

 can seldom be made ideally perfect ; and next, because, 

 if all the counteracting contingencies, whether of fre- 

 quent or of rare occurrence, were included, the rules 

 would be too cumbrous to be apprehended and re- 

 membered by ordinary capacities, on the common 

 occasions of life. The rules of art do not attempt to 

 comprise more conditions than require to be attended 

 to in ordinary cases, and are therefore always imper- 

 fect. In the manual arts, where the requisite condi- 

 tions are not numerous, and where those which the 

 rules do not specify are generally either plain to 



