De rationibus Spiritussancti Lib. II

Paris: P. Gromors, 1543. Early 19th-century gilt-ruled glazed tan calf (Antoine Chaumont, see below; hinges neatly repaired), flat spine with a gilt cross in four compartments and a vertically gilt-lettered green morocco label, all edges gilt, ruled in red.

Only Edition, divided into two books, each with twelve chapters. "A work in which Postel attempts to prove that there is nothing in religion that is not in conformity with nature and with reason" (Caillet, tr.). In the first section, Postel outlines his personal summation of the tenets of the Christian faith and in the second similarly addresses the actions that define a Christian life. Together they reinforce his belief that the fundamental method for the communication of religious truth must be rational demonstration.
            These two dozen essays openly express his growing, highly personal, mysticism and his irenic ideals, which "aroused the hostility of both political and religious authority" (Bouwsma).
            The year 1543 was pivotal in Postel's life. Prior to that, he had been widely admired at court, for instance, holding the post of Royal Reader to François I. But his brush with political intrigue in 1542 cost him his livelihood, and the arrest of his principal patron, Chancellor Poyet in late in the year forced Postel to publish On the Holy Spirit at his own expense, economically typeset in a dense small italic. 
            THIS BOOK APPEARED WITHOUT A PRIVILEGE. The theological faculty of the Sorbonne refused to approve it, and shortly after its appearance, Postel left France, not to return for eight years, during which time he was compelled to flee Rome, later was incarcerated there and, between, spent time with prominent Protestants in Switzerland. Though critical of Reformers, Muslims and Jews, On the Holy Spirit sought to unite the human race under the Christian creed. Indeed, the book is dedicated "To the inhabitants of the whole world" (Ad universi orbis incolas). A good large copy (one or two lower margins uncut), elegant engraved oval bookticket of Antoine Chaumont (fl. 1799-1821), whom Brunet praised (Manuel I: xli; see Flety's Dictionnaire des relieurs 43 & Devauchelle's La Reliure en France II: 112 & 224).
¶Caillet, Manuel bibliographique des sciences...occultes 8907; Bouwsma, Concordia Mundi: The Career and Thought of Guillaume Postel [v] & 300; Postel, Les Écrits de Guillaume Postel publiés en France et leurs éditeurs 1538-1579 14-15 & 47-9; Cioranesco 17813.