Truths, Essay IV. c. 5) already asserted that the knowledge of the causal relation has its ground in the nature of the faculty of knowledge itself. Quite recently Thomas Brown, in his very tediously composed book, “Inquiry into the Relation of Cause and Effect,” 4th edit., 1835, says much the same thing, that that knowledge springs from an innate, intuitive, and instinctive conviction; thus he is at bottom upon the right path. Quite unpardonable, however, is the crass ignorance on account of which in this book of 476 pages, of which 130 are devoted to the refutation of Hume, absolutely no mention is made of Kant, who cleared up the question more than seventy years ago. If Latin had remained the exclusive language of science such a thing would not have occurred. In spite of Brown’s exposition, which in the main is correct, a modification of the doctrine set up by Maine de Biran, of the empirical origin of the fundamental knowledge of the causal relation, has yet found acceptance in England; for it is not without a certain degree of plausibility. It is this, that we abstract the law of causality from the perceived effect of our own body upon other bodies. This was already refuted by Hume. I, however, have shown that it is untenable in my work, “_Ueber den Willen in der Natur_” (p. 75 of the second edition, p. 82 of the third), from the fact that since we apprehend both our own and other bodies objectively in spatial perception, the knowledge of causality must already be there, because it is a condition of such perception. The one genuine proof that we are conscious of the law of causality _before all experience_ lies in the necessity of making a _transition_ from the sensation, which is only empirically given, to its _cause_, in order that it may become perception of the external world. Therefore I have substituted this proof for the Kantian, the incorrectness of which I have shown. A most full and thorough exposition of the whole of this important subject, which is only touched on here, the _a priori_ nature of the law of causality and the intellectual nature of empirical perception, will be found in my essay on the principle of sufficient reason, § 21, to which I refer, in order to avoid the necessity of repeating here what is said there. I have also shown there the enormous difference between the mere sensation of the senses and the perception of an objective world, and discovered the wide gulf that lies between the two. The law of causality alone can bridge across this gulf, and it presupposes for its application the two other forms which are related to it, space and time. Only by means of these three combined is the objective idea attained to. Now whether the sensation from which we start to arrive at apprehension arises through the resistance which is suffered by our muscular exertion, or through the impression of light upon the retina, or of sound upon the nerves of the brain, &c. &c., is really a matter of indifference.