I develop a theory of counterfactuals about relative computability, i.e. counterfactuals such as 'If the validity problem were algorithmically decidable, then the halting problem would also be algorithmically decidable,' which is true, and 'If the validity problem were algorithmically decidable, then arithmetical truth would also be algorithmically decidable,' which is false. These counterfactuals are counterpossibles, i.e. they have metaphysically impossible antecedents. They thus pose a challenge to the orthodoxy about counterfactuals, which would treat them as uniformly true. What’s more, I (...) argue that these counterpossibles don’t just appear in the periphery of relative computability theory but instead they play an ineliminable role in the development of the theory. Finally, I present and discuss a model theory for these counterfactuals that is a straightforward extension of the familiar comparative similarity models. (shrink)

Several authors believe that metaethicists ought to leave their comfortable armchairs and engage with serious empirical research. This paper provides partial support for the opposing view, that metaethics is rightly conducted from the armchair. It does so by focusing on debunking arguments against robust moral realism. Specifically, the article discusses arguments based on the possibility that if robust realism is correct, then our beliefs are most likely insensitive to the relevant truths. These arguments seem at first glance to be dependent (...) on empirical research to learn what our moral beliefs are sensitive to. It is argued, however, that this is not so. The paper then examines two thought experiments that have been thought to demonstrate that debunking arguments might depend on empirical details and argues that the conclusion is not supported. (shrink)