 The dogmatic metaphysicians preceding him, Kant argued, imagined that they could demonstrate the truth of their doctrines in rigorous mathematical fashion, but metaphysical concepts lacked the precision and intelligibility of mathematical concepts. At the same time, they put their trust in intellectual intuition, which was no more certain than the visionary and mystical writings of Emmanuel Swedenborg, who had set down his hallucinations and angelic dictations in twelve volumes of the Arcana Coelestia (1749–56), which Kant read in 1765 and satirized in his Dreams of a Spirit Seer in 1766. Leibniz’s monadology exemplified both errors, for Leibniz thought that, merely by rationally considering the problem of the divisibility of matter, he could demonstrate that the basic constituents of the universe were not material particles obeying the laws of mechanics, but living or at least minded beings with perception and appetite, acting for the good of the universe. At the same time, the details of his picture of the world behind the appearances, incorporating slumbering monads, confused omniscience, and the pre-established harmony, seemed to Kant gratuitous fancies.