The prepositional phrases with sur are so diverse semantically that one may doubt that they evidence or retain any semantic core value that they might share with the preposition: some of them do contribute to producing a setting in which the association of "carrying" and "carried" entities can be recognized (sur la paille, sur la brèche), but other ones are difficult to relate with the core value (partir sur l'heure, sur ces entrefaites), if not difficult to interpret in the first place (sur ordre, sur proposition de). This study show that the core value of the preposition sur consists in connecting an entity with a landmark on the basis of a visual representation in which an invisible dynamic vector of force is introduced, corresponding to...