We propose a rigorous definition of the notion of typicality, making use of the strict partial order naturally induced among the objects at hand by a given concept. This perspective enables us to transpose in the framework of object determination logic some well-known problems like contextual typicality or contextual inference. Then these problems can be treated with the help of the tools developed in the study of non monotonic logics. We show that it is possible to work in a logical formalism, using a new determination connector : the concept f g, when it exists, denotes the determination of the concept f by the concept g. Relatively to this connector, the relation of typical inference between concepts turns out to satisfy the important property of rational monotony. Keywords categorization, concept, objects determination, intension, essence, typicality, contextual inference, rationality, non-monotonic logics.