  Jacobi was born in Düsseldorf, on January 25, 1743, the second son of a well-to-do merchant. His older brother, Johann Georg, was the one selected by the family for an intellectual career, and he did achieve indeed a certain notoriety as a poet in the sentimental style of Gleim. The task of pursuing the commercial activities of the family was reserved for the younger Jacobi. There also were two daughters in the family, half-sisters to Jacobi. Neither of them married, and they eventually took over the management of Jacobi’s household. According to his own account, (Jacobi, 1785: 8; 1787, 67ff; 1789, 328ff ) Jacobi was temperamentally given to extremes of piety from his early youth, and was constantly troubled by questions concerning the existence of God and the endlessness of time. After confirmation, he joined a society of pietists in whose company these tendencies were reinforced. At sixteen, after a brief and disappointing apprenticeship in a Frankfurt commercial house, he was sent in 1759 to Geneva to develop there the social skills required for his appointed vocation. It is in that city that Jacobi, exposed to French ideas, as he matured socially, at the same time also formulated the basic beliefs that were to guide his intellectual career to the end. Under the tutelage of the famous mathematician G.L. Le Sage, he became acquainted with traditional scholastic metaphysics. But he also worked on the writings of Charles de Bonnet, in which he found elements of psychological sensualism combined (allegedly even harmonized) with such Christian beliefs as the after-life, and read Rousseau’s Emile (1761). Appended to the latter was the so titled ‘Profession of Faith of a Savoyard Vicar’, a manifesto upholding the rights of the ‘heart’ against the religion of reason popular among the rationalist philosophers of the day. Jacobi’s resolution, at the time, was never to accept a system of thought unless it could be tested against actual existence and did not contradict his yearnings for God.