Theories of intergenerational justice are a very common and popular way to conceptualise the obligations currently living people may have to future generations. After briefly pointing out that these theories presuppose certain views about the existence, number and identity of future people, I argue that the presuppositions must themselves be ethically investigated, and that theories of intergenerational justice lack the theoretical resources to be able to do this. On that basis, I claim it is necessary to do the ‘ethics of metaphysics’ in order to fully comprehend what, if anything, we may owe future generations. I defend these claims against some important objections.
