title: A zero-one law for random Aboxes authors: B.Ycart and M.C. Rousset abstract: We consider the set of sentences in a decidable fragment of first order logic, restricted to unary and binary predicates, expressed on a finite set of objects. Probability distributions on that set are defined and studied. For large sets of objects, is is shown that under these distributions, random sentences typically have a very particular form, and that all monotone symmetric properties of these random sentences have a probability close to $0$ or $1$. R\'esum\'e : Nous consid\'erons l'ensemble des phrases dans un fragment d\'ecidable de la logique du premier ordre, restreint aux pr\'edicats unaires et binaires, exprim\'e sur un ensemble fini d'objets. Des lois de probabilit\'e sur cet ensemble sont d\'efinies et \'etudi\'ees. Pour de grands ensembles d'objets, on montre que sous ces lois, les phrases al\'eatoires ont une forme particuli\`ere, et que toute propri\'et\'e monotone et sym\'etrique de ces phrases al\'eatoires a une probabilit\'e proche de $0$ ou de $1$. Key words: Description Logics, , Zero-One laws. AMS Subject Classification: 60 F 20.