654 LOGIC OF THE MORAL SCIENCES, 



bination of circumstances by whicli it could be produced. Art then exam- 

 ines these combinations of circumstances, and according as any of them are 

 or are not in human power, pronounces the end attainable or not. The only 

 one of the premises, therefore, which Ait supplies, is the original major 

 premise, which asserts that the attainment of the given end is desirable. 

 Science then lends to Art the proposition (obtained by a series of induc- 

 tions or of deductions) that the performance of certain actions will attain 

 the end. From these premises Art concludes that the performance of these 

 actions is desirable, and finding it also practicable, converts the theorem 

 into a rule or precept. 



§ 3. It deserves particular notice, that the theorem or speculative truth 

 is not ripe for being turned into a precept, until the whole, and not a part 

 merely, of the operation which belongs to science, has been performed. 

 Suppose that we have completed the scientific process only up to a certain 

 point ; have discovered that a particular cause will produce the desired ef- 

 fect, but have not ascertained all the negative conditions which are neces- 

 sary, that is, all the circumstances which, if present, would prevent its pro- 

 duction. If, in this imperfect state of the scientific theory, we attempt to 

 frame a rule of art, we perfoi-m that operation prematurely. Whenever any 

 counteracting cause, overlooked by the theorem, takes place, the rule will be 

 at fault; we shall employ the means and the end will not follow. No ar- 

 guing 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 re-open 

 the investigation to inquire into the remainder of the conditions on which 

 the eifect depends ; and only after we have ascertained the whole of these 

 are we prepai-ed to transform the completed law of the effect into a pre- 

 cept, in which those circumstances or combinations of circumstances 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 pei'fect theory : in the first place, because 

 the theory can seldom be made ideally perfect ; and next, because, if all the 

 counteracting contingencies, whether of frequent 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 imperfect. In the 

 manual arts, where the requisite conditions are not numerous, and where 

 those which the rules do not specify are generally either plain to common 

 observation or speedily learned from practice, rules may often be safely act- 

 ed on by persons who know nothing more than the rule. But in the com- 

 plicated affairs of life, and still more in those of states and societies, rules 

 can not be relied on, without constantly referring back to the scientific laws 

 on which they are founded. To know what are the practical contingen- 

 cies which require a modification of the rule, or which are altogether ex- 

 ceptions to it, is to know what combinations of circumstances would in- 

 terfere with, or entirely counteract, the consequences of those laws ; and 

 this can only be learned by a reference to the theoretic grounds of the rule. 



By a wise practitioner, therefore, rules of conduct will only be consider- 

 ed as provisional. Being made for the most numerous cases, or for those 

 of most ordinary occurrence, they point out the manner in which it will be 

 least perilous to act, where time or means do not exist for analyzing the 



