Kant's proof would, consequently, be reduced to this: that, empirically, we only know _actuality_ of succession; but as besides we recognise _necessity_ of succession in certain series of occurrences, and even know before all experience that every possible occurrence must have a fixed place in some one of these series, the reality and the _à priority_ of the causal law follow as a matter of course, the only correct proof of the latter being the one I have given in § 21 of this work. Parallel with the Kantian theory: that the causal nexus alone renders objective succession and our knowledge of it possible, there runs another: that coexistence and our knowledge of it are only possible through reciprocity. In the "Critique of Pure Reason" they are presented under the title: "Third Analogy of Experience." Here Kant goes so far as to say that "the co-existence of phenomena, which exercise no reciprocal action on one another, but are separated by a perfectly empty space, could never become an object of possible perception"[104] (which, by the way, would be a proof _à priori_ that there is no empty space between the fixed stars), and that "the light which _plays between_ our eyes and celestial bodies"--an expression conveying surreptitiously the thought, that this starlight not only acts upon our eyes, but is acted upon by them also--"produces an intercommunity between us and them, and proves the co-existence of the latter." Now, even empirically, this last assertion is false; since the sight of a fixed star by no means proves its coexistence simultaneously with its spectator, but, at most, its existence some years, nay even some centuries before. Besides, this second Kantian theory stands and falls with the first, only it is far more easily detected; and the nullity of the whole conception of reciprocity has been shown in § 20. [104] Kant, "Krit. d. r. Vern." pp. 212 and 213 of the 1st edition. (English translation, pp. 185 and 186.) The arguments I have brought forward against Kant's proof may be compared with two previous attacks made on it by Feder,[105] and by G. E. Schulze.[106] [105] Feder, "Ueber Raum und Causalität." sect. 29. [106] G. E. Schulze, "Kritik der theoretischen Philosophie," vol. ii. p. 422 _sqq._ Not without considerable hesitation did I thus venture (in 1813) to attack a theory which had been universally received as a demonstrated truth, is repeated even now in the latest publications,[107] and forms a chief point in the doctrine of one for whose profound wisdom I have the greatest reverence and admiration; one to whom, indeed, I owe so much, that his spirit might truly say to me, in the words of Homer: Ἀχλὺν δ' αὖ τοι ἀπ' ὀφθαλμῶν ἕλον, ἣ πρὶν ἐπῆεν.[108] [107] For instance, in Fries' "Kritik der Vernunft," vol. ii. p. 85. [108] I lifted from thine eyes the darkness which covered them before. (Tr.'s Ad.) § 24. _Of the Misapplication of the Law of Causality._