Poetry; on the other hand, practically, either merely to train animals, or for the higher purpose of making human beings dance to its music, when once it has succeeded in discovering which particular wire has to be pulled in order to move each puppet at its pleasure. Now, with reference to the function which effects this, it is quite immaterial whether the intellect turns gravitation ingeniously to account, and makes it serve its purpose by stepping in just at the right time, or whether it brings the collective or the individual propensities of men into play for its own ends. In its practical application we call the Understanding _shrewdness_ or, when used to outwit others, _cunning_; when its aims are very insignificant, it is called _slyness_ and, if combined with injury to others, _craftiness_. In its purely theoretical application, we call it simply _Understanding_, the higher degrees of which are named _acumen_, _sagacity_, _discernment_, _penetration_, while its lower degrees are termed _dulness_, _stupidity_, _silliness_, &c. &c. These widely differing degrees of sharpness are innate, and cannot be acquired; although, as I have already shown, even in the earliest stages of the application of the Understanding, _i.e._ in empirical perception, practice and knowledge of the material to which it is applied, are needed. Every simpleton has Reason--give him the premisses, and he will draw the conclusion; whereas _primary_, consequently intuitive, knowledge is supplied by the Understanding: herein lies the difference. The pith of every great discovery, of every plan having universal historical importance, is accordingly the product of a happy moment in which, by a favourable coincidence of outer and inner circumstances, some complicated causal series, some hidden causes of phenomena which had been seen thousands of times before, or some obscure, untrodden paths, suddenly reveal themselves to the intellect.--