 The three main parts of Aristotle’s great work on logic, the Organon, are represented by the Categories, the Prior and Posterior Analytics and the Topics. The categories (praedicamenta) are not only treated as a formal part of a proposition but also, and most importantly, as universals, which meant that their ontological status also had to be considered. The other two parts of Aristotle’s logic dealt with the problems of how to reach scientific and dialectical conclusions respectively: the Analytics is about finding correct axioms and using them to acquire scientific knowledge; the Topics teaches us how to discuss and treat those issues where it is impossible to attain the truth, so that we have to be satisfied with seeking what is most probable.