Wouldn't the lie you tell yourself in the situation be the best summary of useful behavior, or a utility function, AS a statement of fact? The best way to act is not in any way a statement of fact; but to represent to ourselves a situation and our best course of action in it, we must frequently encode the information as a set of facts. As you say, a full game-theoretical expose of how I should ACT is not possible. Therefore, I represent to myself some useful idea of what the situation IS, not based on its accuracy, but on its utility. This is an AS IF argument.
Wouldn't the lie you tell yourself in the situation be the best summary of useful behavior, or a utility function, AS a statement of fact? The best way to act is not in any way a statement of fact; but to represent to ourselves a situation and our best course of action in it, we must frequently encode the information as a set of facts. As you say, a full game-theoretical expose of how I should ACT is not possible. Therefore, I represent to myself some useful idea of what the situation IS, not based on its accuracy, but on its utility. This is an AS IF argument.