Concept is a central notion in modern philosophy that also influences other disciplines like psychology and linguistics. The author compares modern theories to the work of Aristotle as the first philosopher with an extensive corpus and one of the predecessors both of classical theory and of modal theories of concepts . It is surprising that there is no equivalent term for concept in his work. Both pathma and logos are central to his theory of language and thought. Therefore, this book describes which notion in Aristotle's writing comes closest to concept and whether or not it generates a precise theory.