Within computer program, 1 often will keep around many variables (or pointers) which refer to the same underlying information structure. An identity predicate allows one to ask whether ii variables refer to the equivalent tool. Within numbers of languages, identity may be determined other with efficiency than equality since a previous involves only the pointer comparison when the latter must traverse information structures.

Digital identity

the idsuspire of the individual, class action, tool, run or even any more entity is typically expressed across a digital identifier within a certain context. For instance, the Social Security Number is a digital identifier that identifies a individual inside a context of a U.s.a. social security administration & the internal revenue service. a library-assigned accession total occurs as digital identifier for a particular book inside the context of the library that owns the book.

Direct contrast by using an analogue identifier, like the fingerprint.

Recently, various efforts stand began to define universal digital identifiers, i personally.e. digital identifiers whose context is spherical. URLs are an case of universal digital identifiers for webpage.

The digital identifier is typically utilized jointly by having 1 or even extra credentials that make (believable) assertions all about an take the breath & a digital identifier claimed per suspire. E.g., a charge card total occurs as digital identifier which is typically utilized inside connection by using the charge plate slip & the actual credit card (two come credentials) sequentially to end or even reduce fiscal fraud.

Human identity

Cultural identity

Ethnical identity is the (feeling of) identity of the class action or even culture, or of an individual as far as she/he is influenced by her/his belonging to the class action or even culture. Most common habits, characteristics, ideas can be clear markers of the shared out ethnical identity, however basically these are determined by difference: you sense i personally belong to the class action, & the class action defines itself en bloc, by noticing & highlighting differences by owning more groups & cultures.

Personal identity

People have different physical appearances notably the intimate gender, shape of the face, skin pigmentation, height, and color of hair. A selection of vesture & bodily adornments diverge. Sounds may be utilized for identification: a voice, language, timber, vocabulary, physical movements. Identity can be proved by an identity document. Animal identity may be proved vithe a microchip implant.

Social identity

Logic
Within logic, a identity relation is commonly, (by definition), the transitive, symmetric, and reflexive relation that holds only between the tool & itself. That is, identity is the both-place predicate, "=", such that for all x, y, "x = y" is true iff x is y.

Extra usefully, it may be expressed formally inside second-order logic or in set theory: For all objects x, y, whenever for 100% properties F, Fx iff Fy, so x = y.

These are an axiom of most normal modal logics that for all x, whenever x = x so necessarily ten = x.

(These definitions come naturally unsuitable around a select few front yard of quantified logic, like fuzzy logic and fuzzy set theory, and by having respect to vague objects.)

Metaphysics
Metaphysicians, & for instance philosophers of language & mind, ask more questions: What have a go at it mean for an object to become a equivalent when itself? Whenever x & y come monovular (come a equivalent tool), must it universally exist as monovular? Come it necessarily monovular? What have it off mean for an object to become a equivalent, in case it changes above instance? (Is apple_t a equivalent when apple_t+1?) Whenever an object's area come completely replaced all over period, when in the Ship of Theseus example, in what way would it be a equivalent? The traditional learn from is that of Gottfried Leibniz, who held that x is the equivalent when y whenever & lone in case each predicate true of x is true of y too.

Leibniz's ideas stand steady down in the philosophy of mathematics, where it own influenced a development of the predicate calculus as Leibniz's law. Mathematicians for instance distinguish identity from either equality. Other mundanely, an identity around mathematics may be an equation that holds true for everthing values of the variable.

Further recent metaphysicians own discussed trans-world identity -- a notion that there can be the equivalent object around different conceivable worlds.

Philosophy
Within philosophy, it is crucial to distinguish between qualitative identity & numerical identity.

Arbitrary objects a & b may become said to be qualitatively monovular whenever a & b come duplicates, that is, whenever a & b come exactly similar altogether respects, that is, whenever a & b stand completely qualitative properties in common. Examples of this can become deuce wine glasses mass produced within the equivalent wine glass mill on the equivalent assembly line (at least, for even the relaxed standard of precise similarity), or the carbon atom in a single's left h& and the carbon atom inside of these's best shoulder (possibly avowedly possibly for the virtually all nonindulgent standard of precise similarity).

As an alternative, a & b may exist as said to be numerically monovular whenever a & b come one and the equivalent tool, that is, whenever a is b, that is, whenever there exists single of these tool multifariously known as "a" & "b". For instance, Clark Kent is numerically monovular sustaining Superman in the feel that there exists exclusively 1 human (world health organization happens to have on different textile at different days). This relationship is expressed inside math by using a "=" symbol, e.g., the = b, or even Clark Kent = Superman.