This paper analyzes the rhetoric of futurity at work in a number of texts dealing with the "posthuman future of humanity." It follows these texts in an attempt to historicize such a future in relation to human history. But it also identifies an overwhelming temporal contradiction at the heart of their discourse: that the posthuman is already with us even as it remains to come. If so, is posthuman identity to be interpreted as a mere phase in the history of human subjectivity? Does posthumanity come about in response to ethical and epistemological challenges inherited from the experience of human subjects? Or is it rather an altogether new paradigm that renders the very use of words like "subjectivity," "history," and "experience" anachronistic? Drawing on Hegel, Derrida, and especially Beckett, I argue that an experience of the impossible informs the moment of posthuman self-reflection; and consequently, that the challenge of theorizing a point of contact between human and posthuman being (or human and posthuman history) calls for a new, ad hoc interpretation of the concept of "impossibility."