But this unfortunately can neither be retained nor communicated. The _objective_ conditions of such communication can certainly be presented to others purified and illustrated through plastic and pictorial art, and even much more directly through poetry; but it depends so much upon _subjective_ conditions, which are not at the command of every one, and of no one at all times, nay, indeed in the higher degrees of perfection, are only the gift of the favoured few. Only the worst knowledge, abstract, secondary knowledge, the conception, the mere shadow of true knowledge, is unconditionally communicable. If perceptions were communicable, that would be a communication worth the trouble; but at last every one must remain in his own skin and skull, and no one can help another. To enrich the conception from perception is the unceasing endeavour of poetry and philosophy. However, the aims of man are essentially _practical_; and for these it is sufficient that what he has apprehended through perception should leave traces in him, by virtue of which he will recognise it in the next similar case; thus he becomes possessed of worldly wisdom. Thus, as a rule, the man of the world cannot teach his accumulated truth and wisdom, but only make use of it; he rightly comprehends each event as it happens, and determines what is in conformity with it. That books will not take the place of experience nor learning of genius are two kindred phenomena. Their common ground is that the abstract can never take the place of the concrete. Books therefore do not take the place of experience, because _conceptions_ always remain _general_, and consequently do not get down to the particular, which, however, is just what has to be dealt with in life; and, besides this, all conceptions are abstracted from what is particular and perceived in experience, and therefore one must have come to know these in order adequately to understand even the general conceptions which the books communicate. Learning cannot take the place of genius, because it also affords merely conceptions, but the knowledge of genius consists in the apprehension of the (Platonic) Ideas of things, and therefore is essentially intuitive. Thus in the first of these phenomena the _objective_ condition of perceptive or intuitive knowledge is wanting; in the second the _subjective_; the former may be attained, the latter cannot.