Spatial location and direction are expressed in French primarily by means of prepositional phrases involving three different prepositions:en, dans and à. Disregarding the usual collection of fixed expressions, lexical idiosyncrasies and subtle pragmatic and stylistic effects, the large generalisation about spatial PPs is that dans and a tend to be used with objects understood referentially, as in (1) and (2) (such ‘determinate’ or ‘particularised’ NPs will typically have a determiner in them), while en is used with non-referential objects, as in (3) (these will typically lack a determiner):
(1) a. dans la prison ‘in(to) the prison’
b. dans une prison ‘in(to) a prison’
(2) a l'ecole ‘in(to) the school’
(3) en prison ‘in(to) prison’