In critical theory, the posthuman is a speculative being that represents or seeks to enact a re-writing of what is generally conceived of as human. It is the object of posthumanist criticism, which critically questions Renaissance humanism, a branch of humanist philosophy which claims that human nature is a universal state from which the human being emerges; human nature is autonomous, rational, capable of free will, and unified in itself as the apex of existence. Thus, the posthuman recognizes imperfectability and disunity within him or herself, instead understanding the world through context and heterogeneous perspectives while maintaining intellectual rigour and a dedication to objective observations of the world. Key to this posthuman practice is the ability to fluidly change perspectives and manifest oneself through different identities. The posthuman, for critical theorists of the subject, has an emergent ontology rather than a stable one; in other words, the posthuman is not a singular, defined individual, but rather one who can "become" or embody different identities and understand the world from multiple, heterogeneous perspectives.^[1]

The posthuman, and posthumanism with it, are philosophical positions that overlap and are constantly engaged with much of postmodern philosophy, process philosophy, emerging technologies, and evolutionary biology, so the field is constantly changing. The critical notion of the posthuman is isolated from these fields as the embodiment of critical engagement itself; that is to say that the posthuman is not necessarily human in the first place, but is rather an embodied medium through which critical consciousness is manifested

http://en.wikipedia.org/wiki/Posthuman