1. Spinoza was the negative starting point of Jacobi’s philosophizing. In his work “_On the Doctrine of Spinoza, in letters to Moses Mendelssohn_” (1785), he directed public attention again to the almost wholly forgotten philosophy of Spinoza. The correspondence originated thus: Jacobi made the discovery that Lessing was a Spinozist, and announces this to Mendelssohn. The latter will not believe it, and thence grew the farther historical and philosophical examination. The positive philosophic views which Jacobi exhibits in this treatise can be reduced to the following three principles: (1) Spinozism is fatalism and atheism. (2) Every path of philosophic demonstration leads to fatalism and atheism. (3) In order that we may not fall into these, we must set a limit to demonstrating, and recognize faith as the element of all metaphysic knowledge. (1.) Spinozism is atheism, because, according to it, the cause of the world is no person—is no being working for an end, and endowed with reason and will—and hence is no God. It is fatalism, for, according to it, the human will regards itself only falsely as free. (2.) This atheism and fatalism is, however, only the necessary consequence of all strictly demonstrative philosophizing. To conceive a thing, says Jacobi, is to refer a thing to its nearest cause; it is to find a possible for an actual, the condition for a conditioned, the mediation for an immediate. We conceive only that which we can explain out of another. Hence our conceiving moves in a chain of conditioned conditions, and this connection forms a mechanism of nature, in whose investigation our understanding has its immeasurable field. However far we may carry conception and demonstration, we must hold, in reference to every object, to a still higher one which conditions it; where this chain of the conditioned ceases, there do conception and demonstration also cease; till we give up demonstrating we can reach no infinite. If philosophy determines to apprehend the infinite with the finite understanding, then must it bring down the divine to the finite; and here is where every preceding philosophy has been entangled, while it is obviously an absurd undertaking to attempt to discover the conditions of the unconditioned, and make the absolutely necessary a possible, in order that we may be able to construct it. A God who could be proved is no God, for the ground of proof is ever above that which is to be proved; the latter has its whole reality from the former. If the existence of God should be proved, then God would be derived from a ground which were before and above him. Hence the paradox of Jacobi; it is for the interest of science that there be no God, no supernatural and no extra or supramundane being. Only upon the condition that nature alone is, and is therefore independent and all in all, can science hope to gain its goal of perfection, and become, like its object itself, all in all.