In the seventeenth century, a new kind of public sphere emerged in the Dutch Republic. Courtly structures of political advice made room for new, republican forms of public consultation between the sovereign powers and the general citizenry. Missing, however, were guidelines for how and when to address questions of public import, how to shape citizens sufficiently unprejudiced and in possession of their own free judgment to speak up for themselves in public deliberations, and how to ensure that citizens would candidly engage in public speech with the best interest of the republic in mind, and not simply pursue their private advantage with deception and flattery. This book argues that Spinoza’s freedom of philosophizing and the systematic theory he developed to defend it in his 1670 Tractatus theologico-politicus were conceived to provide just such guidelines. It shows how he understood the freedom of philosophizing as a collective style of reasoning and argument based on mutual teaching and advising, providing a model for the public sphere in a free republic. The book studies the conditions under which Spinoza believed such a public sphere of free philosophizing would flourish, including democratic-republican realignment of the structures of political counsel and sovereign command, popular reform of civic education and instruction in the arts and sciences, establishment of a national religion allowing better regulation of a multi-religious society, and the teaching of theological and political doctrines of universal faith and social contract designed to promote the practice of true religion and prevent citizens from persecuting each other.