Resolving a puzzle about the fixity of the past

In his 2022 article 'A puzzle about the fixity of the past', Lampert argues that standard views concerning knowledge and the semantics of 'actually' conflict with a widely held principle concerning the fixity of the past. I show that his attempt to establish the conflict fails, as it rests on the implicit assumption that a past mental state or utterance involving a modal indexical must have the same content across worlds with a shared past, when in fact it must, given its character, differ in content.