To define life in terms of the notion of the boundary (Grenze; sometimes translated as ‘limit’) was Plessner’s fortunate choice. In his bio-philosophy from 1928 (Die Stufen des Organischen und der Mensch; the title means ‘the levels of the organic and the human being’), he explains how the cell by means of its membrane 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 and to what lies inside. It becomes a living thing. Only then does it allow its environment to appear in it and it to appear in its environment. This philosophy of organic being constitutes the foundation of Plessner’s philosophical anthropology, which moves from plants through animals to the human being. Plessner defines human beings as that kind of living being that is placed ‘in’ the boundary between its body and a corresponding environment. This is the human being’s ‘positionality’, which he shares with all living things. What distinguishes human beings from other living entities is that they are eccentrically positioned: the human being is at a distance to her boundary, and therefore open to the world. From their eccentric position, human beings have to establish artificial boundaries and also embody these boundaries. Plessner puts the thesis of eccentric positionality to the test in the areas of society, history, politics, language, art, music, and generally within the scope of the expressivity of the human body.
The socio-philosophical perspective demonstrates how human beings cope with their precarious boundary situation—open to themselves, but also reciprocally open to the penetrating gaze of the other—through conceding to each person the right to wear ‘masks’, i.e., to play social roles, and through 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 means ‘power and human nature’)), Plessner describes how entire cultures follow the principle of an ‘artificial narrowing of their horizon’. The human condition is characterized by indeterminate relationships to the self, to others, and to the world. Therefore human beings establish spheres of trust, and acknowledge among themselves a duty for ‘politics’, 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 horizon. 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 objective dimension of the human being’s ‘boundary problematic’. His Ästhesiologie des Geistes (1923; the title means ‘the aesthesiology of the spirit’) and his Anthropologie der Sinne (1970; ‘anthropology of the senses’) bring to light what the senses in their diversity accomplish. These accomplishments precede and form the basis of our cognitive access to the world. Through proprioception we are in touch with ourselves as bodily beings, through seeing we are at a distance both from our body and from the external world, and through hearing we resonate with both the external and the social, ‘shared’ world (Mitwelt). Positioned eccentrically between mind and body, the person is capable of rationally abstracting from his sensuous existence, without, however, completely detaching himself from it. Indeed, the opposite is the case. The eccentrically positioned human being pushes the different senses to ever greater accomplishments (in mathematical geometry, fine arts, or 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 to realize an ‘artificial unity of the senses’, whereby language forms a precarious center between distance-producing representation and immediate expression.
Finally, the notion of eccentric positionality takes us to an anthropology of the subjective dimension of human existence. In the enigmatic and ineffable expression of a laughter bursting with joy or an uncontrollable crying, Plessner identifies forms of behavior that are only suitable for a living subject who, in a permanently fragile relation to his own body, must find self-control and a sense of meaning in all possible life situations (Lachen und Weinen, 1941, translated as Laughing and Crying, 1970). In times of crisis, that is, in those ‘boundary predicaments’ that do not make sense and therefore are ‘unanswerable’, the body takes over from the mind the function of answering the question of the situation. 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 does show the characteristic of ‘distance from expression in expression’.
Plessner’s anthropological, sociological, and aesthetic research includes examinations of the myth of the ‘German spirit’. His work Die Verspätete Nation (1935/1959; the title means ‘the belated nation’), documents his efforts on this topic. From a sociocultural perspective, Plessner describes a historically contingent—albeit rich in consequences—specific structure of the ‘bourgeois spirit’, to which he refers as ‘worldly piety’ (Weltfrömmigkeit). Worldly piety is based on a 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) according to the tradition of idealism, the contradictions of existence within the medium of spirit, thus realizing the very best in the human being. 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 final solutions in times of great practical upheaval.
From its very first confrontation with Kant’s critical philosophy onwards (Krisis der transzendentalen Wahrheit im Anfang, 1918; the title means ‘the crisis of transcendental truth in its origin’), Plessner’s work has aimed at formulating a ‘concept of philosophy’ according to which the ground of philosophical reassurance lies not in knowledge guaranteed by pure reason, nor in the primacy of action, but in a ‘philosophical power of judgment’ (1920). Such a power of judgment would effect a delicate balancing act on the boundary between what is inner and what is outer and would therefore answer to the precariousness of ‘human dignity’. And finally this power of judgment is a medium for the development of a practical scepticism.