The paper concerns the understanding of plurals in the framework of Artificial Intelligence and emphasizes the role of time. The construction of collection(s) and their evolution across time is often crucial and has to be accounted for. The paper contrasts a "de dicto" collection where the collection can be considered as persisting over these situations even if its members change with a "de re" collection whose composition does not vary through time. It expresses different criteria of choice between the two interpretations (de re and de dicto) depending on the context of enunciation.
