 Insofar as morality is practical, it should be accessible to and attainable by agents like us: if a theory is too demanding, or relies on intuitions, judgments, motivations, or capacities that people do not (or, worse, cannot) possess, we might on those grounds dismiss it. On the other hand, morality is also normative: it aims not just to describe what we actually do or think, but to guide our practice. For this reason, some philosophers have responded to experimental results claiming to show that attaining and reliably expressing virtues in a wide variety of situations is difficult (see section 3.1 below for a discussion of this literature) by pointing out that the fact that people do not always make the right judgment, or perform actions for the right reasons, does not falsify a theory—it simply shows that people often act in ways that are morally deficient. We will return to these issues when we discuss criticisms of experimental moral philosophy at the end of this entry; for now, we mention them to illustrate that the extent to which experimental moral philosophy challenges traditional philosophical approaches is itself a controversial issue. Some moral philosophers see themselves as deriving moral principles a priori, without appeal to contingent facts about human psychology. Others see themselves as working within a tradition, going back at least as far as Aristotle, that conceives of ethics as the study of human flourishing. These philosophers have not necessarily embraced experimental moral philosophy, but many practitioners envision their projects as outgrowths of the naturalistic moral theories developed by Aristotle, Hume, and others.