Two quotes from Derek Parfit on what he calls empty questions.
Consider, for example, clubs. Suppose that a certain club exists for several years, holding regular meetings. The meetings then cease. Some years later, some of the members of this club form a club with the same name, and the same rules. We ask: ‘Have these people reconvened the very same club? Or have they merely started up another club, which is exactly similar?’ There might be an answer to this question. The original club might have had a rule explaining how, after such a period of non-existence, it could be reconvened. Or it might have had a rule preventing this. But suppose that there is no such rule, and no legal facts, supporting either answer to our question. And suppose that the people involved, if they asked our question, would not give it an answer. There would then be no answer to our question. The claim ‘This is the same club’ would be neither true nor false.
Derek Parfit: Reasons and Persons, p. 213-4.
Though there is no answer to our question, there may be nothing that we do not know. This is because the existence of a club is not separate from the existence of its members, acting together in certain ways. The continued existence of a club just involves its members having meetings, that are conducted according to the club’s rules. If we know all the facts about how people held meetings, and about the club’s rules, we know everything there is to know. This is why we would not be puzzled when we cannot answer the question, ‘Is this the very same club?’ We would not be puzzled because, even without answering this question, we can know everything about what happened. If this is true of some question, I call this question empty.
When we ask an empty question, there is only one fact or outcome that we are considering. Different answers to our question are merely different descriptions of this fact or outcome. This is why, without answering this empty question, we can know everything that there is to know. In my example we can ask, ‘Is this the very same club, or is it merely another club, that is exactly similar?’ But these are not here two different possibilities, one of which must be true.
When an empty question has no answer, we can decide to give it an answer. We could decide to call the later club the same as the original club. Or we could decide to call it another club, that is exactly similar. This is not a decision between different views about what really happened. Before making our decision, we already knew what happened. We are merely choosing one of two different descriptions of the very same course of events.
I must now distinguish between two ways in which a question may be empty. About some questions we should claim both that they are empty, and that they have no answers. We could decide to give the questions answers. But it might be true that any possible answer would be arbitrary. If this is so, it would be pointless and might be misleading to give such an answer. (…)
There is another kind of case in which a question may be empty. In such a case this question has, in a sense, an answer. The question is empty because it does not describe different possibilities, any of which might be true, and one of which must be true. The question merely gives us different descriptions of the same outcome. We could know the full truth about this outcome without choosing one of these descriptions. But if we do decide to give an answer this empty question, one of these descriptions is better than the others. Since this is so, we can claim that this description is the answer to this question. (…)
Derek Parfit: Reasons and Persons, p. 260.