FRIEDRICH HEINRICH JACOBI (1743-1819), a distin-guished writer on philosophy, was born at Dusseldorf on the 25th January 1743. The second son of a wealthy merchant, who owned an extensive sugar factory near Dusseldorf, he was educated for a commercial career, partly in his native place, partly at Frankfort-on-the-Main. At the age of sixteen he was sent to complete his training at Geneva, where he remained for four years. Of a retiring disposition, and far more inclined to thoughtful meditation than to practical activity, Jacobi mainly associated himself at Geneva with the literary and scientific circle of which the most prominent member was Lesage. He studied closely the works of Bonnet, the Swiss naturalist and metaphysician, and was brought into contact with the new political ideas of Bousseau and Voltaire. In 1763 he was called back to Dusseldorf, and in the following year he married and took his place at the head of the mercantile concern handed over to him by his father. After a short period he gave up his commercial career, and in 1770 became a member of the council for the duchies of Juliers and Berg, in which capacity he distinguished himself by his ability in the management of financial affairs, and his zeal in the direction of social reforms. Like his contemporary Hemsterhuis, whom he resembles in many points, Jacobi kept up his interest in literary and philosophic matters by an extensive correspondence, and his mansion at Pempelfort, near Diisseldorf, was the centre of a distin-guished literary circle. With Wieland he contributed to start a new literary journal, the Mercury, in which some of his earliest writings, mainly on practical or economical subjects, were published. Here too appeared in part the first of his philosophic works, the Correspondence of All-will (Allwill's Brief-Sammlung, 1774), a combination of romance with speculation, containing a remarkable delinea-tion of that which we may call the principle of the early romantic school in Germany. This was followed in 1779 by Woldemar, a philosophic novel, of very imperfect struc-ture, but full of genial speculation, and giving the most complete picture of Jacobi's method of philosophizing. In 1779 he was invited to Munich as member of the privy council, but after a short stay there differences with his colleagues and with the authorities of Bavaria drove him back to Pempelfort. A few unimportant tracts on ques-tions of theoretical politics were followed in 1785 by the work which first brought Jacobi directly into relation with the contemporary philosophical public. A conversation which he had held with Lessing in 1780, in which Lessing avowed that he knew no philosophy, in the true sense of that word, save Spinozism, led him to a protracted study of Spinoza's works, while his statement of Lessing's con-fession induced a correspondence with Moses Mendelssohn. The Letters on Spinoza's Theory (Briefe iiber die Lehre Spinoza's, 1785 ; 2d ed., much enlarged and with important Appendices, 1789) expressed sharply and clearly Jacobi's strenuous objection to a demonstrative system in philosophy, and drew upon him the vigorous enmity of the Berlin clique, whose philosophic protagonist was Moses Mendelssohn. Jacobi was ridiculed as endeavouring to reintroduce into philosophy the antiquated notion of unreasoning belief, was denounced as an enemy of reason, as a pietist, and as in all probability a Jesuit in disguise, and was especially taken to task for his employment of the ambiguous term " belief " (Glaube, which may mean belief in the ordinary sense, or faith in the specifically theological significance). Mendels-sohn's reply showed little more than the writer's very slight acquaintance with the Spinozistic system to which he had so frequently and so earnestly appealed, and his mortification at the public disclosure of the fact that he had remained in entire ignorance that Spinoza's Opera Posthuma contained the Ethics is said to have hastened his death.
Jacobi's next important work, David Hume on Belief, or Idealism and Realism, a dialogue (David Hume iiber den Glauben, oder Idealismus und Realismus, 1785), was an attempt to show not only that the term Glaube had been used by the most eminent writers to denote what he had employed it for in the Letters on Spinoza, but that the nature of the cognition of facts as opposed to the con-struction of inferences could not be otherwise expressed. In this writing, and especially in the Appendix, Jacobi came into contact with the critical philosophy, and sub-jected the Kantian view of knowledge to searching ex-amination.
The outbreak of the war with the French republic induced Jacobi in 1793 to leave his home at Diisseldorf, and for nearly ten years he resided in Holstein. While there he became intimately acquainted with Eeinhold, in whose Beitrage, pt. iii., 1801, his important work On the Endeavour of the Critical Philosophy to bring Reason to Understanding was first published, and with Matthias Claudius, the author of the Wandsbecher Bote. During the same period the excitement caused by the accusation of atheism brought against Fichte at Jena led to the publication of Jacobi's Letter to Fichte, in which he made more precise the relation of his own philosophic principles to theology.
Soon after his return to Germany, Jacobi received a call to Munich in connexion with the new academy ot sciences just founded there. The loss of a considerable portion of his fortune induced him to accept this offer; he settled in Munich in 1804, and in 1807 became president of the academy. In 1811 appeared his last philosophic work, directed against Schelling specially, On Divine Things (Von den göttlichen Dingen), the first part of which, a review of the Wandsbecker Bote, had been written in 1798. A bitter reply from Schelling was left without answer by Jacobi, but gave rise to an animated controversy in which Fries and Baader took prominent part. In 1812 Jacobi retired from the office of president, and began to prepare a collected edition of his works. He died before this was completed, on 10th March 1819. The edition of bis writings was continued by his friend Koppen, and was completed in 1825. The works fill six volumes, of which the fourth is in three parts. To the second is prefixed an introduction by Jacobi, which is at the same time an intro-duction to his philosophy. The fourth volume has also an important preface.
The philosophy of Jacobi presents itself as in no way a system, indeed, as, from its principle, essentially unsystematic. A certain fundamental view which underlies all his thinking is brought to bear in succession upon those systematic doctrines which appear to stand most sharply in contradiction to it, and any positive philo-sophic results are given only occasionally. The leading idea of the whole is that of the complete separation between understanding and apprehension of real fact. For Jacobi understanding, or the logical faculty, is purely formal or elaborative, and its results never transcend the given material supplied to it. From the basis of immediate experience or perception thought proceeds by comparison and abstraction, establishing connexions among facts, but remaining in its nature mediate and finite. The principle of reason and con-sequent, the necessity of thinking each given fact of perctption as conditioned, impels understanding towards an endless series of identical propositions, the records of successive comparisons and abstractions. The province of the understanding is therefore strictly the region of the conditioned ; to it the world must present itself as a mechanism. If, then, there is objective truth at all, the existence of real facts must be made known to us otherwise than through the logical faculty of thought; and, as the regress from conclusion to premises must depend upon something not itself capable of logical grounding, mediate thought implies the conscious-ness of immediate truth. Philosophy therefore must resign the hopeless ideal of a systematic (i.e., intelligible) explanation of things, and must content itself with the examination of the facts of consciousness. It is a mere prejudice of philosophic thinkers, a prejudice which has descended from Aristotle, that mediate or demonstrated cognition is superior in cogency and value to the im-mediate perception of truths or facts.
The fundamental principle of Jacobi's system, thus sketched, presents a most interesting analogy with that which has become familiar in English philosophy through the writings of Sir W. Hamilton, upon the historical relations between the two thinkers nothing requires here to be said. No reader of Hamilton can fail to be made aware of the great obligations the Scotch psychologist was under to his German predecessor. But attention to the results of Jacobi's fundamental doctrine, as these were wrought out by com-parison of it with the speculative systems of Spinoza, Kant, and Schelling, will throw great light upon Hamilton's writings, and make clear the connexions of the several parts which in his imper-fect expositions too frequently remained in obscurity.
As Jacobi starts with the doctrine that thought is partial and limited, applicable only to connect facts, but incapable of explain-ing their existence, it is evident that for him any demonstrative system of metaphysic which should attempt to subject all existence to the principle of logical ground must be repulsive. Now in modern philosophy the first and greatest demonstrative system of metaphysic is that of Spinoza, and it lay in the nature of things that upon Spinoza's system Jacobi should first direct his criticism. A summary of the results of his examination is thus presented (Werke, i. 216-223):"(1) Spinozism is atheism; (2) the Kab-balistic philosophy, in so far as it is philosophy, is nothing but unde-veloped or confused Spinozism ; (3) the philosophy of Leibnitz and Wolff is not less fatalistic than that of Spinoza, and carries a resolute thinker to the very principles of Spinoza ; (4) every demonstrative method ends in fatalism ; (5) we can demonstrate only similarities (agreements, truths conditionally necessary), proceeding always in identical propositions ; every proof presupposes something already proved, the principle of which is immediately given (Offenbarung, revelation, is the term here employed by Jacobi, as by many later writers, e.g., Lotze, to denote the peculiar character of an immedi-ate, unproved truth) ; (6) the keystone (Element) of all human knowledge and activity is belief (Glaube). Of these propositions only the first and fourth require further notice. Jacobi, accepting the law of reason and consequent as the fundamental rule of demon-strative reasoning, and as the rule explicitly followed by Spinoza, points out that, if we proceed by applying this principle so as to recede from particular and qualified facts to the more general and abstract conditions, we land ourselves, not in the notion of an active, intelligent creator of the system of things, but in the notion of an all-comprehensive, indeterminate Nature, devoid of will or intelligence. Our unconditioned is either a pure abstraction, or else the impossible notion of a completed system of conditions. In either case the result is atheism, and this result is necessary if the demonstrative method, the method of understanding, is regarded as the only possible means of knowledge. Moreover, the same method inevitably lands in fatalism. For, if the action of the human will is to be made intelligible to understanding, it must be thought as a conditioned phenomenon, having its sufficient ground in preceding circumstances, and, in ultimate abstraction, as the outflow from nature which is the sum of conditions. But this is the fatalist conception, and any philosophy which accepts the law of reason and consequent as the essence of understanding is fatalistic. Thus for the scientific understanding there can be no God and no liberty. It is impossible that there should be a God, for if so he would of necessity be finite. But a finite God, a God that is known, is no God. It is impossible that there should be liberty, for if so the mechanical order of phenomena, by means of which they are com-prehensible, would be disturbed, and we should have an unintelli-gible world, coupled with the requirement that it shall be understood.
Cognition, then, in the strict sense, occupies the middle place between sense perception, which is belief in matters of sense, and reason, which is belief in supersensuous fact. (Jacobi wavered much in his terminology, especially with respect to the word reason ; but even at this stage of his thinking the distinctions just named are sufficiently apparent.) Such a view, and especially the fundamental peculiarity that the categories of the understanding are to be regarded as mere forms of the conditioned, from their very nature limited and relative, presented a certain analogy to the critical philosophy, and accordingly, in the second period of Jacobi's speculative development, he is driven to a comparison of his doc-trines with those of Kant.
His adverse criticism of the Kantian doctrines was directed on three points mainly, and, though in itself but ill-founded, it deserves the careful consideration of all Kantian students. (1) The categories of the understanding and the forms of intuition supply a blank scheme for the given element of sense. But if the given element be merely sensation, and not actually the external thing, we are still, Jacobi thinks, within the position of subjective idealism. At no point in the whole process do we ever get beyond empty form, bare identity. The synthetical unity of consciousness, if no reality be supplied in regard to which it may operate, is mere repetition of the form of conjunction, mere possibility of cognition. Whence do we obtain the reality, the objectivity, of knowledge ? To Jacobi it seemed that Kant, in the second edition of the Kritik, made an effort to demonstrate the external reality of phenomena of experi-ence, and he views the change in Kant's doctrine as the effect of his own critical comments. Nevertheless such demonstration still seems to him unsatisfactory; it yields only the thought-form of externality, not externality in fact. (2) Jacobi agrees with Kant so far as the critical view of the incapacity of understanding to encompass the ideas is concerned, but he thinks Kant in error in supposing that such incapacity results from the subjective limitation of our power of thinking and not from the nature of the categories of understanding in themselves. At the same time he holds that Kant treats the ideas unjustly, and that in his view of reason he tends to make that faculty inferior to understanding. (3) Kant's moral theory is as little satisfactory as his theory of perception. Here, too, in the demand for universally valid law as the law of a will that is its own content, Jacobi can find but the form and not the reality of a universal rule. The universal will is void of con-tent, and the sharp opposition which in the Kantian ethics appears between the ethical motive and all modes of feeling is the natural result of mere formalism. When Jacobi endeavours to supply the place of the Kantian theorems which he rejects, the inherent weak-ness of his own principle becomes apparent. External things are known to us by immediate perception, a combination of intuition and belief. The principle of inference to realities is that of cause and effect, the significance of which we learn from observing the relation between our will and changes in the objective world, and this principle by a natural necessity we extend to all existence. The infinite progress from consequents to grounds, which is the form of procedure of understanding, yields no conclusion as regards the being of a God. But when we regard the whole system of real things, we are compelled to infer a real cause, which, from the significance of the causal principle, is seen to be of necessity an active intelligent will, a God who foresees events. This apprehension of God is faith, reason, or feeling, as Jacobi, following Fries, is willing to call it.
Not even in his latest work of importance (Von den göttlichen Dingen), which is specifically on religion, does Jacobi manage to make clear the step, which he has himself characterized as the salto mortale of the human intellect, from the finite to the infinite ; still less the further difficulty as to the possibility of holding that the God who for cognition is the unknown God must be held to possess providence, personality, life. He acknowledges that this is anthropomorphic, bitterly assails Schelling for identifying divine and human reason, but leaves the problem standing. The truth is that what Jacobi called feeling, and regarded as immediate knowledge, is not a simple act of mind, capable of yielding simple results, but the very essence of complex thinking. We cannot separate know-ledge of things from apprehension of them in the way he has adopted. Nor can the human reason rest satisfied with a system devoid of inner coherence and harmony.
The best introductions to Jacobi's philosophy are the preface to the second vol. of the Works, and Appendix 7 to the Letters on Spinoza's Theory. There are two monographs of some extent upon him :Kuhn, Jacobi und die Philosophie seiner Zeit, 1834; and Zirngiebl, F. II. Jacobi's Leben, Dichten, und Denken. 1867. See also F. H. Jacobi's Auserlesener Briefwechsel, 2d ed., by Roth, 2 vols., 1825-27; and Gildemeister1 s edition of Hamann's Schriften, vol. v. (R. AD.)