In connection with Kant we must here begin by speaking of Jacobi， whose philosophy is contemporaneous with that of Kant； in both of these the advance beyond the preceding period is very evident. The result in the two cases is much the same， although both the starting point and the method of progression are somewhat different. In Jacobi's case the stimulus was given mainly by French philosophy， with which he was very conversant， and also by German metaphysics， while Kant began rather from the English side， that is， from the scepticism of Hume. Jacobi， in that negative attitude which he preserved as well as Kant， kept before him the objective aspect of the method of knowledge， and specially considered it， for he declared knowledge to be in its content incapable of recognizing the Absolute： the truth must be concrete， present， but not finite. Kant does not consider the content， but took the view of knowledge being subjective； and for this reason he declared it to be incapable of recognizing absolute existence. To Kant knowledge is thus a knowledge of phenomena only， not because the categories are merely limited and finite， but because they are subjective. To Jacobi， on the other hand， the chief point is that the categories are not merely subjective， but that they themselves are conditioned. This is an essential difference between the two points of view， even if they both arrive at the same result.
Friedrich Heinrich Jacobi， born at Düsseldorf in 1743， held office first in the Duchy of Berg， and then in Bavaria. He studied in Geneva and Paris， associating in the former place with Bonnet and in the latter with Diderot. Jacobi was a man of the highest character and culture. He was long occupied with State affairs， and in Düsseldorf he held a public office which was connected with the administration of the finance department in the State. At the time of the French Revolution he was obliged to retire. As a Bavarian official he went to Munich， there became President of the Academy of Sciences in 1804， which office he， however， resigned in 1812； for in the Napoleonic period Protestants were decried as demagogues. He lived at Munich till the end of his life， and died at the same place on the 10th of March， 1819.(1)In the year 1785， Jacobi published Letters on Spinoza， which were written in 1783， on the occasion of the dispute with Mendelssohn above-mentioned (p. 406)； for in none of his writings did Jacobi develop his philosophy systematically， he set it forth in letters only. When Mendelssohn wished to write a life of Lessing， Jacobi sent to ask him if he knew that “Lessing was a Spinozist”
(Jacobi's Werke， Vol. IV. Sec. 1， pp. 39， 40). Mendelssohn was displeased at this， and it was the occasion of the correspondence. In the course of the dispute it was made evident that those who held themselves to be professed philosophers and possessed of a monopoly of Lessing's friendship， such as Nicolai， Mendelssohn， &c.， knew nothing about Spinozism； not only was there manifested in them the superficial character of their philosophic insight， but ignorance as well； with Mendelssohn， for instance， this was shown respecting even the outward history of the Spinozistic philosophy， and much more regarding the inward (Jacobi's Werke， Vol. IV. Sec. 1， p. 91). That Jacobi asserted Lessing to be a Spinozist， and gave a high place to the French - this serious statement came to these good men as a thunderbolt from the blue. They - the self-satisfied， self-possessed， superior persons - were quite surprised that he also made pretensions to knowledge， and of such a “dead dog” as Spinoza (ibidem， p. 68). Explanations followed upon this， in which Jacobi further developed his philosophic views.
Mendelssohn is directly opposed to Jacobi， for Mendelssohn took his stand on cognition， placed true existence immediately in thought and conception， and maintained： “What I cannot think as true does not trouble me as doubt. A question which I do not understand， I cannot answer， it is for me as good as no question at all."(2) He continued to argue on these same lines. His proof of the existence of God thus carries with it this necessity of thought， viz. that actuality must plainly be in thought， and a thinker must be pre-supposed， or the possibility of the actual is in the thinker. “What no thinking Being conceives as possible is not possible， and what is thought by no thinking creature as actual cannot be actual in fact. If we take away from anything whatsoever the conception formed by a thinking Being that that thing is possible or actual， the thing itself is done away with.”
The Notion of the thing is thus to man the essence of the same. “No finite Being can think the actuality of a thing in its perfection as actual， and still less can he perceive the possibility and actuality of all present things. There must thus be a thinking Being or an understanding which in the most perfect way thinks the content of all possibilities as possible， and the content of all actualities as actual； i.e. there must be an infinite understanding， and this is God."(3) Here on the one hand we see a unity of thought and Being， on the other the absolute unity as infinite understanding - the former is the self-consciousness which is apprehended as finite merely. Actuality， Being， has its possibility in thought， or its possibility is thought； it is not a process from possibility to actuality， for the possibility remains at home in the actuality.
Jacobi maintains against these demands of thought - and this in one view is the chief thought in his philosophy - that every method of their demonstration leads to fatalism， atheism， and Spinozism，(4) and presents God as derived and founded upon something else； for comprehending Him signifies demonstrating His dependence. Jacobi thus asserts that mediate knowledge consists in giving a cause of something which has in its turn a finite effect， and so on； so that a knowledge such as this can all through relate to the finite only.
