Logic, a short writing by Faust Vrančić, was published in 1608 in Venice for the first time. The revised and broadened edition came out in 1616 'in Venice as well. Starting from the definition of logic as ars discendi et docendi scientias and from the division of logic into three unit (each of them deals with one of the logical instruments), and after, having discussed the terms and statements, Vrančić deals with each of three logical instruments separately, i.e. with definitions in the first unit, with divisions in ,the second unit and with argumentations in the third one. Standing on the ground that has been inherited from Arilstotel, he opposes, however, both the contemporary peripatetic understanding of logic, and the rhetorical logic of the 16th century. That critical aspect is particularly perceptible in two passages added to the unit on definitions, De praedicamentis and De metaphysica. Vrančić rejects the metaphysical (ontological) understanding of logic, in accordance with which the predicaments would be summa genera omnium entium, and he excludes the substance from predicaments. He also rejects the possibility of metaphysicy as a science. Different substances are the subjects of different sciences, and there is no science that would deal with substance or being itself. Delivering logic from metaphysics and ontology in that way, he makes it possible for logic to be formed purely and only by means of its own instruments. There, as well, lies the reason for the critics of rhetorical logic, e.g. because it confuses the psychological and the logical matters while deviding logic into inventio and iudicio. Such a separation of logic from the other disciplines and its forming from itself on its own basis is not just the matter of past. It is, in its reall sense, a new, modern principle.