The founder of phenomenology, the German philosopher Edmund Husserl, introduced the term in his book Ideas: A General Introduction to Pure Phenomenology (1913; trans. 1931). Early followers of Husserl such as the German philosopher Max Scheler, influenced by his previous book, Logical Investigations (1900-1; trans. 1970), claimed that the task of phenomenology is to study essences, such as the essence of emotions. Although Husserl himself never gave up his early interest in essences, he later held that only the essences of certain special conscious structures are the proper object of phenomenology. As formulated by Husserl after 1910, phenomenology is the study of the structures of consciousness that enable consciousness to refer to objects outside itself. This study requires reflection on the content of the mind to the exclusion of everything else. Husserl called this type of reflection the phenomenological reduction. Because the mind can be directed toward nonexistent as well as real objects, Husserl noted that phenomenological reflection does not presuppose that anything exists, but rather amounts to a bracketing of existence, that is, setting aside the question of the real existence of the contemplated object.
What Husserl discovered when he contemplated the content of his mind were such acts as remembering, desiring, and perceiving and the abstract content of these acts, which Husserl called meanings. These meanings, he claimed, enabled an act to be directed toward an object under a certain aspect; and such directedness, called intentionality, he held to be the essence of consciousness. Transcendental phenomenology, according to Husserl, was the study of the basic components of the meanings that make intentionality possible. Later, in Cartesian Meditations (1931; trans. 1960), he introduced genetic phenomenology, which he defined as the study of how these meanings are built up in the course of experience.
All phenomenologists follow Husserl in attempting to use pure description. Thus, they all subscribe to Husserl's slogan To the things themselves. They differ among themselves, however, as to whether the phenomenological reduction can be performed, and as to what is manifest to the philosopher giving a pure description of experience. The German philosopher Martin Heidegger, Husserl's colleague and most brilliant critic, claimed that phenomenology should make manifest what is hidden in ordinary, everyday experience. He thus attempted in Being and Time (1927; trans. 1962) to describe what he called the structure of everydayness, or being-in-the-world, which he found to be an interconnected system of equipment, social roles, and purposes.
Because, for Heidegger, one is what one does in the world, a phenomenological reduction to one's own private experience is impossible; and because human action consists of a direct grasp of objects, it is not necessary to posit a special mental entity called a meaning to account for intentionality. For Heidegger, being thrown into the world among things in the act of realizing projects is a more fundamental kind of intentionality than that revealed in merely staring at or thinking about objects, and it is this more fundamental intentionality that makes possible the directness analyzed by Husserl.
The French existentialist Jean Paul Sartre attempted to adapt Heidegger's phenomenology to the philosophy of consciousness, thereby in effect returning to Husserl. He agreed with Husserl that consciousness is always directed at objects but criticized his claim that such directedness is possible only by means of special mental entities called meanings. The French philosopher Maurice Merleau-Ponty rejected Sartre's view that phenomenological description reveals human beings to be pure, isolated, and free consciousnesses. He stressed the role of the active, involved body in all human knowledge, thus generalizing Heidegger's insights to include the analysis of perception. Like Heidegger and Sartre, Merleau-Ponty is an existential phenomenologist, in that he denies the possibility of bracketing existence. See EXISTENTIALISM. Phenomenology has had a pervasive influence on 20th-century thought. Phenomenological versions of theology, sociology, psychology, psychiatry, and literary criticism have been developed, and phenomenology remains one of the most important schools of contemporary philosophy.