Hybrid theories, psychological plausibility, and the human/animal divide

A hybrid theory is any moral theory according to which different classes of individuals ought to be treated according to different principles. We argue that some hybrid theories are able to meet standards of psychological plausibility, by which we mean that it's feasible for ordinary human beings to understand and act in accord with them. Insofar as psychological plausibility is a theoretical virtue, then, such hybrid theories deserve more serious consideration. To make the case for this view, we explain what psychological plausibility is and why we might value it, why the human/animal divide appears to be an entrenched feature of human psychology, and why Robert Nozick's hybrid theory doesn't go far enough. Finally, we make the case that a more promising psychologically plausible hybrid theory, with respect to humans and animals, will be (at least) at tribrid theory-that is, positing three domains rather than two.