The article presents and describes a manuscript volume which contains some unknown speeches of the famous antitrinitarian thinker, Ernst Soner. Beside the data of the book and the short description of the speeches, the first one is discussed in detail, which is about libertas philosophandi, and emphasizes the importance of criticism and detachment, prefiguring rational thinking. The work is a new proof for the thesis that the rediscovered ancient scepticism was not the only source of early modern rationalism.