This dissertation examines the conceptual emergence of posthumanism and probes the viability of posthumanist redefinitions of the human (self). Motivated by a sense of the simultaneous necessity and danger of the desire to revise our notion of the human in light of the contemporary ecological crisis, it establishes the genealogy of posthumanism (recording its rise out of antihumanism, philosophical skepticism, and scientific materialism) and assesses the strange subjectivity that posthumanism calls for us to inhabit. It studies three pictures of the posthuman self (humans as matter, humans as animals, humans as networks) derived from the discoveries of three sciences (physics, biology, cybernetics) and claimed by three posthumanist theories (new materialism, animal studies, actor-network theory). Inspired by ordinary language philosophy, it analyzes the relationship of these posthuman pictures of the self to what Stanley Cavell, following Ludwig Wittgenstein, calls skepticism: the desire, both natural and unnatural, to deny and transcend the human and its conditions of sense-making. It asks whether these skeptical visions of the human self can be lived and answers by putting each posthumanist theory into dialogue with a fictional work that dramatizes its vision: Jean-Marie Gustave Le Clézio’s Terra amata (1967), Michel Houellebecq’s La Possibilité d’une île (2005), and Maurice Dantec’s Grande Jonction (2006). It argues that these works illustrate how posthumanist theories risk devolving into an unlivable skepticism regarding human life through their overextension of scientific knowledge to define the human individual and through their avoidance of the ordinary. In doing so, this dissertation intervenes in debates surrounding the status of scientific knowledge and its import for ordinary life, the value and price of skepticism, the nature and legacy of humanism, and the future of the humanities as an anthropocentric discipline.