The pantheism controversy was an event in German cultural history which had an impact throughout Europe.
A conversation between philosopher Friedrich Heinrich Jacobi and dramatist Gotthold Lessing in 1780 led Jacobi to a protracted study of Spinoza's works. Lessing had avowed that he knew no philosophy, in the true sense of that word, save Spinozism. At that particular time and place,[where?] Spinozism was the equivalent of atheism.
Jacobi's Briefe über die Lehre Spinozas (Letters on the Teachings of Spinoza (1785); 2nd, enlarged edition with important appendices: 1789) expressed sharply and clearly Jacobi's strenuous objection to a dogmatic system in philosophy, and drew upon him the vigorous enmity of the Berlin group, led by Moses Mendelssohn.
Jacobi claimed that Spinoza's doctrine was pure materialism, because all Nature and God are said to be nothing but extended substance. This, for Jacobi, was the result of Enlightenment rationalism and it would finally end in absolute atheism. Moses Mendelssohn disagreed with Jacobi, saying that there is no actual difference between theism and pantheism. The entire issue became a major intellectual and religious concern for European civilization at the time, which Immanuel Kant rejected, as he thought that attempts to conceive of transcendent reality would lead to antinomies in thought.
Jacobi was ridiculed for trying to reintroduce into philosophy the antiquated notion of unreasoning belief, was denounced as an enemy of reason, as a pietist, and as a Jesuit in disguise, and was especially attacked for his use of the ambiguous term Glaube (German: "belief").
His next important work, David Hume Über den Glauben, oder Idealismus und Realismus (1787), 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 construction of inferences could not be otherwise expressed. In this writing, and especially in the appendix, Jacobi came into contact with the critical philosophy, and subjected the Kantian view of knowledge to searching examination.
The attraction of Spinoza's philosophy to late eighteenth-century Europeans was that it provided an alternative to materialism, atheism, and deism. Three of Spinoza's ideas strongly appealed to them:
- the unity of all that exists;
- the regularity of all that happens; and
- the identity of spirit and nature.