A conversation between the German philosopher Friedrich Heinrich Jacobi and the German dramatist Gotthold Ephraim Lessing in 1780 had led Jacobi to a protracted study of Baruch Spinoza's works.

Lessing had avowed that he knew no philosophy, in the true sense of that word, save Spinozism.

Jacobi's Über die Lehre des Spinozas (1st ed. 1785, 2nd ed. 1789) expresses sharply and clearly his strenuous objection to a dogmatic system in philosophy, and draws upon him the vigorous enmity of the Berlin group, led by Moses Mendelssohn.

Jacobi claims that Spinoza's doctrine is pure materialism, because all Nature and God are said to be nothing but extended substance.

This, for Jacobi, is the result of Enlightenment rationalism and it will finally end in absolute atheism.

Mendelssohn disagrees with Jacobi, saying that there is no actual difference between theism and pantheism.

The entire issue becomes a major intellectual and religious concern for European civilization at this time, which Immanuel Kant rejects, as he thinks that attempts to conceive of transcendent reality will lead to antinomies in thought.

Jacobi is ridiculed for trying to reintroduce into philosophy the antiquated notion of unreasoning belief, is denounced as an enemy of reason, as a pietist, and as a Jesuit in disguise, and is especially attacked for his use of the ambiguous term Glaube (German: "belief, faith").