 In the case of indexical expressions, it is hard to see what feature of the meaning of ‘now’, if any, plays both of these two roles. This poses a problem for the Fregean doctrine of senses. Later theorists have rejected the feature of sense or modes of presentation whereby they determine reference, while retaining the idea a single object or property can have multiple modes of presentation. (See Chalmers 2002). In rejecting the idea that modes of presentation determine referents by themselves, they say that reference is determined by mode of presentation plus select facts about the environment in which the utterance or experience are had.