AbstractIn Theory and Practice Kant challenges the well-worn view that practitioners do not need to rely on theory. He acknowledges that experts with a deep knowledge of theory may fail as practitioners both in technical matters, and in matters of morality and justice. However, since action-guiding theories are intended to shape rather than to fit the world, practitioners have no point of reference other than the theories or principles that they seek to enact. If theories of duty appear to offer too little guidance for action, they should look for more rather than fewer principles, which will enable them to guide their practical judgement with greater, if still incomplete, specificity.