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Alterity is a philosophical and anthropological term meaning "otherness", that is, the "other of two" (Latin alter).  It is also increasingly being used in media to express something other than "sameness," an imitation compared to the original.  Alterity is an encounter with "the other." This "other" is not like any other worldly object or force. The perceiving subject (I myself) sees that another human being is "like me." They act like I do, appear to be in control of their conscious life, just like me. The "other" takes me out of myself and creates new understanding, that is, alterity. Philosophically, the life of the other functions symbolically. It is in our encounter with this other life that generates the contrasts at the foundations of new consciousness.  In such exchanges we are not lost, but rather the "proper self," one's subjectivity, scrubbed and brightly lit, becomes stained and unsure by a renewed understanding from a nonoriginal origin. Ego is still there; we do not disappear, but boundaries are less well defined. The self is opened to new experiences, and the "affair" of the other is made available." 
Within the phenomenological tradition, alterity is usually understood as the entity in contrast to which an identity is constructed, and it implies the ability to distinguish between self and not-self, and consequently to assume the existence of an alternative viewpoint. The concept was further developed by Emmanuel Levinas in a series of essays, collected in Altérité et transcendence (Alterity and Transcendence) (1995).
For Cornelius Castoriadis (L'institution imaginaire de la société, 1975; The Imaginary Institution of Society, 1997) radical alterity/otherness (French: altérité radicale) denotes the element of creativity in history: "For what is given in and through history is not the determined sequence of the determined but the emergence of radical otherness, immanent creation, non-trivial novelty."
For Jean Baudrillard (Figures de l'alterité, 1994; Radical Alterity, 2008), alterity is a precious and transcendent element and its loss would seriously impoverish a world culture of increasing sameness and "arrogant, insular cultural narcissism."
According to Spivak, it is imperative for one to uncover the histories and inherent historical behaviors in order to exercise an individual right to authentic experience, identity and reality. Within the concept of socially constructed histories one "must take into account the dangerous fragility and tenacity of these concept-metaphors."
Spivak recalls her personal history: "As a postcolonial, I am concerned with the appropriation of 'alternative history' or 'histories'. I am not a historian by training. I cannot claim disciplinary expertise in remaking history in the sense or rewriting it. But I can be used as an example of how historical narratives are negotiated. The parents of my parents' grandparents' grandparents were made over, not always without their consent, by the political, fiscal and educational intervention of British imperialism, and now I am independent. Thus I am, in the strictest sense, a postcolonial."
Spivak explains four "master words" to identify the modes of being that create alterity: "Nationalism, Internationalism, Secularism and Culturalism." Furthermore, tools for developing alternative histories include: "gender, race, ethnicity, class".
Jeffery Nealon, in Alterity Politics: Ethics and Performative Subjectivity, argues that "ethics is constituted as an inexorable affirmative response to different identities, not through an inability to understand or totalize the other."
There is included a long article on alterity in the University of Chicago's Theories of Media: Keywords Glossary by Joshua Wexler. Wexler writes: "Given the various theorists formulations presented here, the mediation of alterity or otherness in the world provides a space for thinking about the complexities of self and other and the formation of identity."
The concept of alterity is also being used in theology and in spiritual books meant for general readers. This is not out of place because, for believers in the Judeo-Christian tradition, God is the ultimate 'Other'. Alterity has also been used to describe the goal of many Christians, to become themselves deeply "other" than the usual norms of behavior and patterns of thought of the secular culture at large. Enzo Bianchi in Echoes of the Word expresses this well, "Meditation always seeks to open us to alterity, love and communion by guiding us toward the goal of having in ourselves the same attitude and will that were in Christ Jesus."
Jadranka Skorin-Kapov in The Aesthetics of Desire and Surprise: Phenomenology and Speculation, relates alterity or otherness to newness and surprise, "The signification of the encounter with otherness is not in its novelty (or banal newness); on the contrary, newness has signification because it reveals otherness, because it allows the experience of otherness. Newness is related to surprise, it is a consequence of the encounter... Metaphysical desire is the acceptivity of irreducible otherness. Surprise is the consequence of the encounter. Between desire and surprise there is a pause, a void, a rupture, an immediacy that cannot be captured and presented."
The term has gained further use in seemingly somewhat remote disciplines, e.g. historical musicology where it is employed by John Michael Cooper in a study of Johann Wolfgang von Goethe and Felix Mendelssohn.