A vast majority of marketing theory and research has focused on relativism and idealism in order to understand ethical behavior. However, making ethical assessments that in turn influence behavior is much more complicated than it appears. One of the most important developments in contemporary philosophy has been the renewed interest in epistemic virtue. Epistemologists contend that belief is an ethical process that is susceptible to the intellectual virtue or vice of one’s own life and personal experiences. Open-mindedness, curiosity, careful thinking, (...) creativity, and intellectual courage are the foundations of epistemic virtues. Closed-mindedness, intellectual overconfidence, unimaginativeness, intellectual conformity, and wishful thinking are among epistemic vices. The purpose of this investigation is to introduce epistemology to marketing ethics by linking it to personal moral philosophies (idealism and relativism) and optimism to explain various ethically challenging organizational behaviors. The items of epistemology were developed and pretested by the lead author of this study. Structural equations (LISREL) analyses found that epistemic virtues and vices are better predictors of ethical behavior than were personal moral philosophies (idealism and relativism), and their influence on mild and severe levels of unethical behaviors was enhanced by the moderator variable, optimism. Implications are designed to develop suggestions for improving ethical behavior in the workplace. (shrink)