 In Avicenna’s theory of logic, second intentions are defined as the properties of concepts which these concepts acquire when used in attaining knowledge, for example: being a subject or being a predicate, being a premise or being a syllogism. Avicenna thus confirms that logic has a proper subject matter, and hence becomes a full-fledged part of philosophy, and not only a tool for the philosophical disciplines (Sabra 1980, 752–753). Avicenna’s definition of logic appears already in Dominicus Gundisalvi (De divisione philosophiae 150). Further Latin writers to adopt Avicenna’s thesis that the subject matter of logic is second intentions are Roger Bacon and Thomas Aquinas, followed by many subsequent authors such as Pseudo-Robert Kilwardby, Radulphus Brito, Hervaeus Natalis, Peter Aureoli, Duns Scotus and William of Ockham (Knudsen 1982; Maierù 1987; Perler 1994).