LOGIC OF PRACTICE, OR ART. 5S9 



die olJ-fashioned German tacticians who were vanquLshcd l»y Napoleon, 

 or the physician who preterroil that his patients should di«; l)y rule 

 rather tiian recover contrary to it, is rightly judged to he a mrrv ped- 

 ant, and the slave of his formulas. 



Now, the reasons of a maxim of policy, or of any other rule of art, 

 caji be no other than the theorems of the coriesponding science. 



The relation in whicli rules of art staml to doctrines of science may 

 be thus characterized. The art proposes to itself an end to be at- 

 tained, defmes the end, and hands it over to the science. The science 

 receives it, considers it as a phenomenon or eflect to be studied, and 

 having investigated its causes and conditions, sends it back to Art with 

 a theorem of the combinations of circumstances by which it could be 

 produced. Art then examines these combinations of circumslaiiccs, 

 and according as any of them are or arc not in human power, pro- 

 nounces the etid attainable or not. The only one of the premisses, 

 therefore, which Art supplies, is the original major premiss, which a.s- 

 serts that the attainment of the given end is desirable. iScienco then 

 lends to Art the proposition (obtained by a series of inductions or 

 of deductions) that the perlbrmance of certain actions will attain the 

 end. From these premisses Art concludes that the perfonnance of 

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

 theorem into a rule or prccept- 



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

 truth is not ripe for being turned into a precept, until all that ]>art of 

 the operation which belongs to science has been completely performed. 

 Suppose that we have comj)leted the scientific process only up to a 

 certain point ; have discovered that a particular cause will produce 

 the desired effect, but not ascertained all the negative conditi(tns which 

 are necessary, that is, all the circumstances which, if present, would 

 prevent its production. If, in this imperfect state of the scientific the- 

 ory, we attempt to frame a rule of ait, we perfoi-m that operati(m 

 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 arguing from or about the 

 rule itself will then help us through the difficulty : there is notliing for 

 it but to turn back and finish the scientific process which should have 

 preceded the formation of the rule. We- nnist reopen the investigation, 

 to inquire into the remainder of the conditions upon which the effect 

 depends ; and only after we have a.scertained tlu; whole of these, are 

 we prepared 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, ruli-s must be formed 

 from something less than this ideally peifect theory; in the first ])lace, 

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

 because, if all the counteracting contingencies, whether of fiequi-nt or 

 of rare occurrence, were inchuhMl, the rules would be too cund)rous to 

 be apprehended and remembered by ordinaiy capacities, on the com- 

 mon occasions of life. The ndes of ait do not attempt tr> comprise more 

 conditions than require to be attemled to in ordinary cases, and arc 

 theref(jre always impei-fect. In tlw manual arts, where the requisite 

 conditions are not numerous, and where those which the rules do not 



