Much of the difficulty of Levinas' writing derives from the complexity of his prose and the deceptive familiarity of his key terms. He is best known both in France and internationally as a philosopher of ethics, and the problems of comprehension that his writing raises cluster in particular around the significance of ethics in his thought. Ethics, in his use of the term, is neither a code of rules nor the study of reasoning about how we ought to act. The first use of the word éthique in the original preface to the 1961 edition of Totality and Infinity informs us, in a pronouncement that is as enigmatic as it is axiomatic, that 'ethics is an optics' (TI, 8/23). The context tells us more about what this does not mean than what it does; and the later qualification that 'Ethics is the spiritual optics' (TI, 76/78) might be thought to confuse the issue even further. Whatever ethics might be, it also entails a disturbance of the very language in which ethical inquiry will be pursued.

The first use of the word éthique in the main text of Totality and Infinity is perhaps the most quoted passage of the book, and one which reveals a great deal about Levinas' approach:

A calling into question [mise en question] of the Same - which cannot occur [se faire] within the egoistic spontaneity of the Same - is brought about [se fait] by the Other [l'Autre]. We name this calling into question of my spontaneity by the presence of the Other [Autrui] ethics. The strangeness of the Other, his irreducibility to the I [Moi], to my thoughts and my possessions, is precisely accomplished [s'accomplit] as a calling into question of my spontaneity, as ethics. Metaphysics, transcendence, the welcoming of the Other by the Same, of the Other by Me, is concretely produced [se produit] as the calling into question of the Same by the Other, that is, as the ethics that accomplishes [accomplit] the critical essence of knowledge. (TI, 33/43)

Colin Davis, Levinas: An Introduction, 35-36