The Epistolae are the correspondence of the Dutch philosopher Benedictus de Spinoza with a number of well-known learned men and with Spinoza's admirers, which Spinoza's followers in Amsterdam published after his death in the Opera Posthuma (Dutch translated edition: De nagelate schriften, 1677).Spinoza preserved the letters he received as well as the rough drafts of the letters he sent; 88 letters about mostly philosophical subjects have been preserved: 50 by Spinoza and 38 by his correspondents, 52 written in Latin and 26 in Dutch. The letters concern subjects from the works by Spinoza (for instance infinity and the attributes (properties) of "God", Spinoza's concept of the universe) but also about ghosts and scientific discoveries as the vacuum. Source: Wikipedia (en)