KIE: Gillon outlines the principles of the deontological, or duty-based, group of moral theories in one of a series of British Medical Journal articles on the philosophical foundations of medical ethics. He differentiates between monistic theories, such as Immanuel Kant's, which rely on a single moral principle, and pluralistic theories, such as that of W.D. Ross, which rely on several principles that potentially could conflict. He summarizes the contributions of Kant and Ross to the development of deontological thought, then concludes his essay with brief paragraphs on other deontological approaches to the resolution of conflicting moral principles.