 Sometimes what a word picks out depends on context. Indexicals (“I”, “you”, “here”, “yesterday”) and demonstratives (“this”, “that”, “over there”) are obvious cases: which thing someone refers to using “this” depends on what they are demonstrating at the time. Kaplan (1989) proposed that these expressions function as rigid designators on occasions of use: whether the proposition expressed by a sentence including one is true at a possible world depends on how things stand with the object, if any, referred to in the actual world. If on 5 March 2020 I say “Yesterday it was sunny”, I express a proposition true at a possible world iff it is sunny on 4 March 2020 in that world. Elvis says “I was born in 1935”: that is true at a possible world iff Elvis was born in 1935 there.