For the periodical publication "Identity", see Identity (magazine).
In metaphysics, identity is 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 applet the same as applet+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?
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.
More recent metaphysicians have discussed trans-world identity -- the notion that there can be the same object in different possible worlds.
Two objects can be called identical, meaning that they have the same shape, size and other properties. Thus, when we interchange the two objects, we do not see any difference. However, in terms of a stricter sense of identity, the initial and final situation are different. By observing not just the initial and final situation but the move itself, we can know this.
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 sociological and political terms, identity is individuals' labeling of themselves as members of particular groups -- such as nation, social class, subculture, ethnicity, gender, and so forth. It is in this sense which sociologists and historians speak of a national identity of a particular country, and feminist and queer theorists speak of gender identity.
Many people feel pride in their identity groups, which furthers a sense of community and belonging. Often they will attempt to add to their identity by behaving in certain ways that have only a superficial connection, often the behavior wasn't even established within the group, but through the stereotypes of oppressors. Though, it should not be mistaken that all people who identify a certain way attempt to add more to it. Identity has been a central element of pride movements such as gay pride or black consciousness, which seek to strengthen politically oppressed groups by improving members' sense of identity. However, many consider a national or ethnic identity as a cultural background for demagoguery, ethnic and religious conflicts, and the like.
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.
Identity might rely on:
- Credit card number 1
- Postcode or Zip code
- Phone number
- National Insurance number (UK) 1
- Fingerprints 1
- Iris in the eye 1
- DNA 1