Defining life in terms of the notion of the boundary (Grenze; sometimes also translated as “limit”) was Plessner’s “fortunate touch.” In his 1928 bio-philosophy, Levels of Organic Life and the Human, he explains how, by means of its membrane, a cell turns into an animate entity within an inanimate environment. Only if a thing takes up a relationship to its boundary, does it become open (in its own characteristic way) to what lies outside of, as well as inside, itself. It becomes a living thing. Only then does its environment appear in it and does it appear in an environment. This philosophy of organic being constitutes the foundation of Plessner’s philosophical anthropology, which moves from plants through animals to the human. For Plessner, the human, like all living beings, is “positioned” within the boundaries of her lived body and in a corresponding environment. This is the characteristic positionality of life. What distinguishes human beings from other living entities is that they are also excentrically positioned: the human being is at a distance from her boundary, and therefore open to the world. From out of their excentric position, human beings have to establish and embody artificial boundaries. Plessner puts his notion of excentric positionality to the test in the areas of society, history, politics, language, art, music, and generally in terms of the expressivity of the human body.
The sociophilosophical strain of Plessner’s work explores how human beings cope with their precarious boundary situation—open to themselves, but also open to the penetrating gaze of the other—by conceding to each person the right to wear “masks,” i.e., to play social roles, and by creating a public sphere that is founded on tact and tactics. In such a public sphere lie The Limits of Community (Grenzen der Gemeinschaft, 1924). In his Political Anthropology (Macht und menschliche Natur, 1931; the title literally translates as “power and human nature”), Plessner describes how entire cultures “artificially narrow their horizons”: because the human condition is characterized by indeterminate relationships to the self, to others, and to the world, human beings establish spheres of trust, and acknowledge among themselves a “political” duty, that is, a duty to maintain the sphere of trust against what is foreign or strange. Groups of human beings become aware of their own historical transformations and of the fact that other communities have other ways of shaping their horizons. They are able to understand that their own culture expresses the unmediated essence of the human being in a mediated way and also that, by virtue of this artificial mediation, their own culture not only uncovers this essence in a particular way but at the same time always hides some of its aspects. Insight into the structural obscurity of the self (i.e., into the human being as homo absconditus) is an insight into the openness of man, which enables human beings to accept the possibility of different horizons without necessarily abandoning their own view of the world.
Plessner examines not only the social but also the material dimension of the human being’s “boundary problem.” His Die Einheit der Sinne: Grundlinien einer Aesthesiologie des Geistes (1923; “The Unity of the Senses: Elements of an Aesthesiology of Spirit”) and his Anthropologie der Sinne (1970; “Anthropology of the Senses”) demonstrate what the senses accomplish in their diversity, preceding and forming the basis of our cognitive access to the world. Proprioception puts us in touch with ourselves as bodily beings; our faculty of sight puts us at a distance both from our body and from the external world; and our faculty of hearing allows us to resonate with both the external and the social, “shared” world (Mitwelt). Positioned excentrically between mind and body, persons are capable of rationally abstracting from their sensuous existence, without, however, completely detaching themselves from it. Indeed, the opposite is the case. The excentrically positioned human being pushes the different senses to ever greater accomplishments (in mathematical geometry, fine arts, music…), thereby approximating the extremity of distance and resonance. Placed in between the two opposite poles of immediate unity and distance, the human being has the task of realizing an artificial “unity of the senses,” whereby language forms a precarious center between distance-producing representation and immediate expression.
Finally, the notion of excentric positionality takes us to an anthropology of the subjective dimension of human existence. In the enigmatic and ineffable expression of joyful laughter or uncontrollable crying, Plessner identifies forms of behavior that only appertain to living subjects who, in a permanently fragile relation to their own bodies, must find self-control and a sense of meaning in all possible life situations (Laughing and Crying, 1970). In times of crisis, that is, in those “boundary predicaments” that leave us without answers, the body takes over from the mind the function of coping with existence. Thus laughing and crying are just as essential to human life as the ability to use language. These forms of behavior represent perhaps an even stronger objection to Cartesian dualism than the linguistic capacity, as they demonstrate that human beings form a unity that is broken and intermittent but not divided into body and mind as separate substances. The same is true of the phenomenon of the smile, which does not refer to a crisis situation, but which displays a “distance in the expression from the expression.”
Plessner’s anthropological, sociological, and aesthetic research includes examinations of the myth of the “German spirit,” the subject of his work Die Verspaetete Nation (1935/1959; “The Belated Nation”). From a sociocultural perspective, Plessner describes a historically contingent albeit fateful structure of the “bourgeois spirit,” which he refers to as “worldly piety” (Weltfroemmigkeit). Worldly piety concerns the Protestant preference for “inwardness” over the externality of politics. In its secular form, this preference awakens in us the expectation that we can appeal to the inwardness of philosophy in order to overcome, or sublate (aufheben) in the tradition of idealism, the contradictions of existence within the medium of spirit, thereby realizing what is best in the human. Since this bourgeois spirit of idealism cannot develop any valid standard to employ in matters of public concern, it is not able to oppose the force of ostensibly permanent solutions in times of great political upheaval.
From its first confrontation with Kant’s critical philosophy onwards (Krisis der transzendentalen Wahrheit im Anfang, 1918; “The Crisis of Transcendental Truth in its Origin”), Plessner’s work sought to formulate a “concept of philosophy” according to which the ultimate ground of philosophical reassurance lies not in knowledge guaranteed by pure reason, nor in the primacy of action, but in “philosophical judgment” (Plessner’s 1920 habilitation was entitled “Toward a Critique of Philosophical Judgment”). Such a power of judgment effects a delicate balancing act on the boundary between inside and outside and thus answers to the precariousness of “human dignity” as well constituting a medium for the development of a practical skepticism.