When we talk about the semantics of prepositional phrases, we are talking about a specific kind of conventionalized pattern. Conventional patterns are arbitrary in the sense that they are not predictable from one language to another. But in another way, they are nevertheless motivated (Sweetser 1990). There is a reason they occur as they do. Basic cognitive processes influence how different prepositions extend from spatial meanings to more abstract ones.

Temporal constructions shift the landmark and the trajector source expressions out of the physical plane and reconceptualize them as events. The trajector is an event conceived as moving away from the landmark viewed as a temporal reference point. Fundamental to temporal expressions with ἐκ and ἀπό are distance and separation, which are then applied to the temporal plane.