In his letter to Henry Oldenburg, which can be dated 1-11 January 1676, Spinoza argues that the concept of fatalis necessitas represents the main foundation of his Ethica. Known by Oldenburg, Boyle and Leibniz, the phrase gave rise to the first attempts to both define and oppose Spinozian determinism. By briefly reexamining the sources of Spinoza’s concept of fatalis necessitas, starting with the elements already highlighted by Oldenburg, Boyle and Leibniz, the article discusses a decisive shift in the history of modern thought. In the years 1675-1676, the crucial topics of predestination and voluntarism, taken up by Spinoza in his frequent references to St Paul, were reread by him and interpreted as «concatenation of causes» and fatalis necessitas, that is to say: reality is thoroughly knowable without resorting to the notion of mystery, i.e., that which goes beyond reason (supra rationem) and constitutes the central nucleus of Christian tradition.
