The word ‘identity’ first came into use in English in the sixteenth century, as a borrowing from French and Latin (Late Latin identitas, from idem, the same). It can denote two rather different conditions of sameness: that which subsists between two or more people or objects, which are ‘identical’ or that of a single person or object having the same distinct qualities or characteristics throughout its existence. Early usages tended to promote the first quality; the second became dominant slightly later.

These definitions might seem at first to contradict each other. One way of understanding them might be to consider that important accessory of modern travel, the passport or ‘identity document’. Such a document enables people to be distinguished as individuals, for instance, by means of a photograph, given name and number, and other details that make them unique. Reference to origin points – date and place of birth, perhaps names of parents – also imply that an individual's identity derives from unique circumstances pertaining to their creation. But passports also ‘identify’ people in a different way: as one of a group of many, perhaps citizens of a state (Caplan and Torpey 2001). Identity documents might further locate individuals in other collective categories such as gender, ethnicity or religion. In short, identity involves having a continuously distinct existence; but can also mean being one of the same ‘kind’ of people or things.

Not all philosophers accept the idea that an individual's identity is fixed and continuous. In the eighteenth century, David Hume (1739–40, I, 439–41) declared personal identity to be a fiction, ‘nothing but a bundle or collection of different perceptions’, sustained by ‘operations of the imagination’. Modern theorists (e.g., Sen 2006; Younge 2010) likewise perceive identity as being an accretion of often potentially contradictory attitudes, sustained by our complex relations with others, and also by the effects of experience, socialization and other normative cultural pressures (tradition, habits and customs) or ‘epistemes’, that is, the social and intellectual apparatus which renders judgement possible. In most modern contexts, identity is acknowledged to be constructed through a mass of social interactions and acts of representation: identity is therefore ‘not an object but a process’ (Schick 1999). Reflecting this, some theorists (e.g., Brubaker and Cooper 2000) advocate the use of the term ‘identification’ over ‘identity’.