There are sentences that express the same temporally fully specified proposition at all contexts--call them 'context-insensitive, temporally specific sentences.' Sentence (1) 'Obama was born in 1961' is a case in point: at all contexts, it expresses the proposition ascribing to the year 1961 the property of being a time in which Obama was born. Suppose that someone uttered (1) in a context located on Christmas 2000 in our world. In this context, (1) is a true sentence about the past. Moreover, it seems impossible that (1) will be false in a successive context (one located, say, on Christmas 2020 in our world). More generally, one might be tempted to endorse the following principle: if a context-insensitive, temporally specific sentence is uttered in a context in which it is about the past and takes a certain truth value in this context, it cannot be the case that it takes a different truth value in a successive context located in the same world. In this paper, we present linguistic evidence that shows that this principle fails. On this basis, we draw an apparently crazy conclusion: the past can change. We then explain why this conclusion is not that crazy, after all.
