Identity

Identity refers to the definition of a subject. It provides the information required to select its subject out of a group; i.e., it "identifies" that subject. A related concept is identification[?], an object that provides information on an identity. Identity is not always intepreted the same way as equality (in any sense) or equivalence[?]; objects that are not identical may be distinct.

In metaphysics, identity refers to the quality of being "the same". Philosophers ask:

• What does it mean for an object to be the same as itself?
• What does it mean for an object to be the same, if it changes over time? (Is apple_t the same as apple_t+1?)
• If an object's parts are entirely replaced over time, as in the Ship of Theseus example, in what way is it the same?

A traditional view is that of Gottfried Leibniz, who held that x is the same as y if and only if every predicate true of x is true of y as well. More recent metaphysicians have discussed trans-world identity[?] -- the notion that there can be the same object in different possible worlds.

Leibniz's ideas have taken root in the philosophy of mathematics, where they have influenced the development of the predicate calculus as Leibniz's law[?]. Mathematicians sometimes distinguish identity from equality. More mundanely, an identity in mathematics may be an equation that holds true for all values of a variable.

In cognition, identity is discussed in terms of whether or not an individual is self-reflective (i.e., whether it is aware of its own identity). For example, in 2002, some papers indicated that dolphins possess the ability to identify themselves in mirrors.

The psychological idea of identity in humans is tied up in self-image[?], one's view or model of oneself. Psychologists and counsellors[?] interest themselves in psychological identity: an individual person's sense of self.

In socio-political terms, identity can refer to individuals' habits of labelling themselves as part of or representing a specific national, social, ethnic or gender-oriented group. Oppressed minorities can take pride in such self-identifying and ideally achieve a sense of community and belonging, as with gay pride or black consciousness[?], for example. Ideas of self-identification[?] are especially important in queer theory. On the other hand, one could speculate that much of the warfare and civil strife occurring since (say) 1789 has identity as its root cause. Identity has been used politically both by groups asserting rights denied them, and by demagogues and nationalists.

To designers of secure computer systems, identity is a core concept of authentication. Identity theft is said to occur when one person gains control of credentials (such as credit card numbers or passwords) which belong to another, thus becoming able to masquerade as the "stolen" identity.