Internal and External Validity in Ethical Reasoning
A particular approach to ethical reasoning has come to dominate much Anglo-American philosophy, one which assumes that the most rigorous method is to proceed by analysis of thought experiments. In thought experiments, features such as context and history are stripped away, and all factors other than those of ethical interest are stipulated to be equal. This chapter argues that even if a thought experiment produces results that are internally valid—in that it provides a genuine ethical insight about the highly controlled and simplified experimental scenario under discussion—this does not imply external validity. Just as in empirical experiments, there is a yawning gap between succeeding in the relatively easy project of establishing internal validity in a controlled and simplified context, and the more difficult one of establishing external validity in the messier and more complex real world.