Alterity is derived from the Latin alteritas, meaning ‘the state of being other or different; diversity, otherness’. Its English derivatives are alternate, alternative, alternation, and alter ego. The term alterité is more common in French, and has the antonym identité ( Johnson and Smith 1990: xviii). The term was adopted by philosophers as an alternative to ‘otherness’ to register a change in the Western perceptions of the relationship between consciousness and the world. Since Descartes, individual consciousness had been taken as the privileged starting point for consciousness, and ‘the “other” appears in these [post-Enlightenment] philosophies as a reduced “other,”as an epistemological question’(xix). That is, in a concept of the human in which everything stems from the notion that ‘I think, therefore I am’, the chief concern with the other is to be able to answer questions such as ‘How can I know the other?’, ‘How can other minds be known?’ The term ‘alterity’ shifts the focus of analysis away from these philosophic concerns with otherness – the ‘epistemic other’, the other that is only important to the extent to which it can be known – to the more concrete ‘moral other’ – the other who is actually located in a political, cultural, linguistic or religious context (xix). This is a key feature of changes in the concept of subjectivity, because, whether seen in the context of ideology, psychoanalysis or discourse, the ‘construction’ of the subject itself can be seen to be inseparable from the construction of its others.

Literary theorists commonly see the most influential use of alterity in Mikhail Bakhtin’s description of the way in which an author moves away from identification with a character (Todorov 1984).The novelist must understand his or her character from within, as it were, but must also perceive it as other, as apart from its creator in its distinct alterity.Importantly,dialogue is only possible with an ‘other’,so alterity, in Bakhtin’s formulation, is not simply ‘exclusion’, but an apartness that stands as a precondition of dialogue, where dialogue implies a transference across and between differences of culture, gender, class and other social categories. This is related to his concept of ‘exotopy’ or ‘outsideness’, which is not simply alienness, but a precondition for the author’s ability to understand and formulate a character, a precondition for dialogue itself. In post-colonial theory,the term has often been used interchangeably with otherness and difference. However, the distinction that initially held between otherness and alterity – that between otherness as a philosophic problem and otherness as a feature of a material and  discursive location – is peculiarly applicable to post-colonial discourse. The self-identity of the colonizing subject, indeed the identity of imperial culture,is inextricable from the alterity of colonized others,an alterity determined, according to Spivak, by a process of othering. The possibility for potential dialogue between racial and cultural others has also remained an important aspect of the use of the word, which distinguishes it from its synonyms.

Source: Post - colonial studies: the key concepts.  Link