Jonathan Pengelly

This thesis shows morality to be broader and more diverse than its human instantiation. It uses the idea of machine morality to argue for this position. Specifically, it contrasts the possibilities open to humans with those open to machines to meaningfully engage with the moral domain. This contrast identifies distinctive characteristics of human morality, which are not fundamental to morality itself, but constrain our thinking about morality and its possibilities. It also highlights the inherent potential of machine morality to be radically different from its human counterpart and the implications this has for the moral significance of machines. My argument is particularly focussed on moral theory, which is the study of the observable and hypothetical conceptual structures of morality. By identifying structures that are recognisably moral in nature but which sit outside the boundaries of human realisation, we have tangible proof that a meaningful distinction exists between human morality and the wider moral domain. This is achieved by showing that certain essentially human limits restrict the conceptual possibilities open to human realisation. The tight coupling between these limits and the existing conceptual structures of human morality also explains why it is unjustifiable to assume that the same structures would be suitable for machines. They do not share these same limits with us, which leads me to conclude that many conceptual structures are quite distinctive to human morality and that the structures of machine morality would be significantly different. Four examples illustrate these conclusions concretely. The first, supererogation, is an example of a moral concept that doesn't easily extend to machines. Human limits dictate what it is reasonable to expect from one another and restrict our ability to pursue aspirational moral goals. I show that machine supererogation, if it is at all possible, would require a very different justificatory basis to be coherent. The second, agency, is an example of a concept whose structures extend beyond the bounds of human realisation. The greater flexibility of artificial identity allows machines to experiment with novel forms of inter- and intra-agency. In comparison, human agency structures are limited by their tight coupling with human conceptions of identity. The third, moral aspiration, is a concept with a distinctive function in human morality. Certain aspirational ends are peculiar in that they are obviously unrealisable and even undesirable, yet their pursuit is instrumentally justifiable. This justification depends on cognitive limits that aren't shared by machines, which leads me to conclude that the role of moral aspiration in machine morality, if there is any, would necessarily differ from its human counterpart. The fourth, moral responsibility, is an example of a concept whose existing practices don't translate over to machines. We don't understand machine agency well enough to be able to judge a machine's culpability or effectively blame it. Consequently, I suggest that a responsibility conception prioritising understanding over blame is a more promising avenue for a shared conception suitable for both humans and machines. This thesis does not speculate about the existence of moral machines. This remains an open question, and one that is largely irrelevant for my conclusions as the idea alone is enough to advance our thinking. It does this by helping us identify the boundaries of human morality, and then, to think beyond them by recognising the possibilities of machine morality.