This makes it clear that “It’s Friday” is true in some possible worlds and false in others, depending on whether my person moment (my current mental state, including all the evidence I have from perception etc) is spatio-temporally located at a Friday in that possible world.
My point is that the choice of your person moment is not part of the data of a possible world, it’s something additional to the possible world. A world contains all sorts of person moments, for many people and at many times, all together. Specifying a world doesn’t specify which of the person moments we are looking at (or from). Whether “It’s Friday” or not is a property of a (world, person-moment) pair, but not of a world considered on its own.
Keeping this distinction in mind is crucial for decision theory, since decisions are shaping the content of the world, in particular multiple agents can together shape the same world. The states of the same agent at different times or from different instances (“person moments”) can coordinate such shaping of their shared world. So the data for preference should be about what matters for determining a world, but not necessarily other things such as world-together-with-one-of-its-person-moments.
My point is that the choice of your person moment is not part of the data of a possible world, it’s something additional to the possible world. A world contains all sorts of person moments, for many people and at many times, all together. Specifying a world doesn’t specify which of the person moments we are looking at (or from). Whether “It’s Friday” or not is a property of a (world, person-moment) pair, but not of a world considered on its own.
Keeping this distinction in mind is crucial for decision theory, since decisions are shaping the content of the world, in particular multiple agents can together shape the same world. The states of the same agent at different times or from different instances (“person moments”) can coordinate such shaping of their shared world. So the data for preference should be about what matters for determining a world, but not necessarily other things such as world-together-with-one-of-its-person-moments.