_Perception_ is not only the _source_ of all knowledge, but is itself knowledge κατ᾽ εξοχην, is the only unconditionally true, genuine knowledge completely worthy of the name. For it alone imparts _insight_ properly so called, it alone is actually assimilated by man, passes into his nature, and can with full reason be called _his_; while the conceptions merely cling to him. In the fourth book we see indeed that true virtue proceeds from knowledge of perception or intuitive knowledge; for only those actions which are directly called forth by this, and therefore are performed purely from the impulse of our own nature, are properly symptoms of our true and unalterable character; not so those which, resulting from reflection and its dogmas, are often extorted from the character, and therefore have no unalterable ground in us. But _wisdom_ also, the true view of life, the correct eye, and the searching judgment, proceeds from the way in which the man apprehends the perceptible world, but not from his mere abstract knowledge, _i.e._, not from abstract conceptions. The basis or ultimate content of every science consists, not in proofs, nor in what is proved, but in the unproved foundation of the proofs, which can finally be apprehended only through perception. So also the basis of the true wisdom and real insight of each man does not consist in conceptions and in abstract rational knowledge, but in what is perceived, and in the degree of acuteness, accuracy, and profundity with which he has apprehended it. He who excels here knows the (Platonic) Ideas of the world and life; every case he has seen represents for him innumerable cases; he always apprehends each being according to its true nature, and his action, like his judgment, corresponds to his insight. By degrees also his countenance assumes the expression of penetration, of true intelligence, and, if it goes far enough, of wisdom. For it is pre-eminence in knowledge of perception alone that stamps its impression upon the features also; while pre-eminence in abstract knowledge cannot do this. In accordance with what has been said, we find in all classes men of intellectual superiority, and often quite without learning. Natural understanding can take the place of almost every degree of culture, but no culture can take the place of natural understanding. The scholar has the advantage of such men in the possession of a wealth of cases and facts (historical knowledge) and of causal determinations (natural science), all in well-ordered connection, easily surveyed; but yet with all this he has not a more accurate and profound insight into what is truly essential in all these cases, facts, and causations. The unlearned man of acuteness and penetration knows how to dispense with this wealth; we can make use of much; we can do with little. One case in his own experience teaches him more than many a scholar is taught by a thousand cases which he _knows_, but does not, properly speaking, _understand_.