Posthumanism mainly differentiates from classical humanism in that it restores the stature that had been made of humanity to one of many natural species. According to this claim, humans have no inherent rights to destroy nature or set themselves above it in ethical considerations a priori. Human knowledge is also reduced to a less controlling position, previously seen as the defining aspect of the world. The limitations and fallibility of human intelligence are confessed, even though it does not imply abandoning the rational tradition of humanism.
Ihab Hassan, critic, scholar, and theorist in the academic study of literature, once stated that "humanism may be coming to an end as humanism transforms itself into something one must helplessly call posthumanism". This view predates the currents of posthumanism which have developed over the past twenty years in somewhat diverse, but complementary, domains of thought and practice. For example, Ihab Hassan is a scholar of literature and a known postmodernist whose theoretical writings expressly address postmodernism in society.
Theorists who both complement and contrast Ihab Hassan include Michel Foucault, Judith Butler, Bruno Latour, Shannon Bell, N. Katherine Hayles, and Douglas Kellner. Among the theorists are philosophers who have written about a "posthuman condition" which is often substituted for the term "posthumanism".
Posthumanism is sometimes used as a synonym for an ideology of technology known as "transhumanism" because it affirms the possibility and desirability of achieving a "posthuman future" in purely evolutionary terms. However, posthumanists in the humanities and the arts are critical of transhumanism, in part, because they argue that it incorporates and extends many of the flaws of Enlightenment humanism, namely scientific imperialism and perfectibilism.
The posthuman or post-human, in critical theory, 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 scientific rigor 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.
The posthuman, and posthumanism with it, are philosophical positions that overlap and are constantly engaged with much of postmodern philosophy, biotechnology, 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.
Steve Nichols published the Post-Human Manifesto in 1988, and holds a contrarian view that human beings are already post-human compared to previous generations.
Critical discourses surrounding posthumanism are not homogeneous, but in fact present a series of often contradictory ideas, and the term itself is contested, with one of the foremost authors associated with posthumanism, Manuel DeLanda, decrying the term as "very silly. Covering the ideas of, for example, Robert Pepperell's The Posthuman Condition, and N Katherine Hayles's How We Became Posthuman under a single term is distinctly problematic due to these contradictions.
The posthuman is roughly synonymous with the "cyborg" of A Cyborg Manifesto by Donna Haraway. Haraway's conception of the cyborg is an ironic take on traditional conceptions of the cyborg that inverts the traditional trope of the cyborg whose presence questions the salient line between humans and robots. Haraway's cyborg is in many ways the "beta" version of the posthuman, as her cyborg theory prompted the issue to be taken up in critical theory.
Following Haraway, N. Katherine Hayles, whose book How We Became Posthuman grounds much of the critical posthuman discourse, asserts that liberal humanism - which separates the mind from the body and thus portrays the body as a "shell" or vehicle for the mind - becomes increasingly complicated in the late 20th and 21st centuries because information technology put the human body in question. Hayles maintains that we must be conscious of information technological advancements while understanding information as "disembodied," that is, something which cannot fundamentally replace the human body but can only be incorporated into it and human life practices.
The posthuman is a being that relies on context rather than relativity, on situated objectivity rather than universal objectivity, and on the creation of meaning through 'play' between constructions of informational pattern and reductions to the randomness of on/off switches, which are the foundation of digital binary systems.