In
philosophy, identity (from , "sameness") is the relation each thing bears only to itself. The notion of identity gives rise to
many philosophical problems, including the
identity of indiscernibles (if ''x'' and ''y'' share all their properties, are they one and the same thing?), and questions about change and
personal identity
Personal identity is the unique numerical identity of a person over time. Discussions regarding personal identity typically aim to determine the necessary and sufficient conditions under which a person at one time and a person at another time ca ...
over time (what has to be the case for a person ''x'' at one time and a person ''y'' at a later time to be one and the same person?). It is important to distinguish between ''qualitative identity'' and ''numerical identity''. For example, consider two children with identical bicycles engaged in a race while their mother is watching. The two children have the ''same'' bicycle in one sense (''qualitative identity'') and the ''same'' mother in another sense (''numerical identity'').
This article is mainly concerned with ''numerical identity'', which is the stricter notion.
The philosophical concept of identity is distinct from the better-known notion of identity in use in
psychology
Psychology is the scientific study of mind and behavior. Psychology includes the study of conscious and unconscious phenomena, including feelings and thoughts. It is an academic discipline of immense scope, crossing the boundaries betwe ...
and the
social science
Social science is one of the branches of science, devoted to the study of societies and the relationships among individuals within those societies. The term was formerly used to refer to the field of sociology, the original "science of soc ...
s. The philosophical concept concerns a
''relation'', specifically, a relation that ''x'' and ''y'' stand in
if, and only if they are one and the same thing, or ''identical to'' each other (i.e. if, and only if ''x'' = ''y''). The
sociological notion of identity, by contrast, has to do with a person's self-conception, social presentation, and more generally, the aspects of a person that make them unique, or qualitatively different from others (e.g.
cultural identity
Cultural identity is a part of a person's identity, or their self-conception and self-perception, and is related to nationality, ethnicity, religion, social class, generation, locality or any kind of social group that has its own distinct cu ...
,
gender identity
Gender identity is the personal sense of one's own gender. Gender identity can correlate with a person's assigned sex or can differ from it. In most individuals, the various biological determinants of sex are congruent, and consistent with the ...
,
national identity
National identity is a person's identity or sense of belonging to one or more states or to one or more nation, nations. It is the sense of "a nation as a cohesive whole, as represented by distinctive traditions, culture, and language". National i ...
,
online identity, and processes of
identity formation). Lately, identity has been conceptualized considering humans’ position within the ecological web of life.
Metaphysics of identity
Metaphysicians and philosophers of language and mind ask other questions:
* What does it mean for an object to be the same as itself?
* If x and y are identical (are the same thing), must they always be identical? Are they ''necessarily'' identical?
* 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?
The
law of identity originates from
classical antiquity
Classical antiquity (also the classical era, classical period or classical age) is the period of cultural history between the 8th century BC and the 5th century AD centred on the Mediterranean Sea, comprising the interlocking civilizations ...
. The modern formulation of identity is that of
Gottfried Leibniz
Gottfried Wilhelm (von) Leibniz . ( – 14 November 1716) was a German polymath active as a mathematician, philosopher, scientist and diplomat. He is one of the most prominent figures in both the history of philosophy and the history of mat ...
, who held that ''x'' is the same as ''y''
if and only if
In logic and related fields such as mathematics and philosophy, "if and only if" (shortened as "iff") is a biconditional logical connective between statements, where either both statements are true or both are false.
The connective is bi ...
every
predicate true of ''x'' is true of ''y'' as well.
Leibniz's ideas have taken root in the
philosophy of mathematics
The philosophy of mathematics is the branch of philosophy that studies the assumptions, foundations, and implications of mathematics. It aims to understand the nature and methods of mathematics, and find out the place of mathematics in peopl ...
, 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.
Hegel
Georg Wilhelm Friedrich Hegel (; ; 27 August 1770 – 14 November 1831) was a German philosopher. He is one of the most important figures in German idealism and one of the founding figures of modern Western philosophy. His influence extends ...
argued that things are inherently self-contradictory and that the notion of something being self-identical only made sense if it were not also not-identical or different from itself and did not also imply the latter. In
Hegel
Georg Wilhelm Friedrich Hegel (; ; 27 August 1770 – 14 November 1831) was a German philosopher. He is one of the most important figures in German idealism and one of the founding figures of modern Western philosophy. His influence extends ...
's words, "Identity is the identity of identity and non-identity." More recent metaphysicians have discussed
trans-world identity ''Transworld Identity'' is the idea that objects exist in multiple possible worlds.
See also
*Identity (philosophy)
*Modal realism
Modal realism is the view propounded by philosopher David Lewis that all possible worlds are real in the same way ...
—the notion that there can be the same object in different possible worlds. An alternative to trans-world identity is the counterpart relation in
Counterpart theory. It is a similarity relation that rejects trans-world individuals and instead defends an objects counterpart – the most similar object.
Some philosophers have denied that there is such a relation as identity. Thus
Ludwig Wittgenstein
Ludwig Josef Johann Wittgenstein ( ; ; 26 April 1889 – 29 April 1951) was an Austrian- British philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy of language. He is cons ...
writes (''
Tractatus'' 5.5301): "That identity is not a relation between objects is obvious." At 5.5303 he elaborates: "Roughly speaking: to say of two things that they are identical is nonsense, and to say of one thing that it is identical with itself is to say nothing."
Bertrand Russell
Bertrand Arthur William Russell, 3rd Earl Russell, (18 May 1872 – 2 February 1970) was a British mathematician, philosopher, logician, and public intellectual. He had a considerable influence on mathematics, logic, set theory, linguistics, ar ...
had earlier voiced a worry that seems to be motivating Wittgenstein's point (''
The Principles of Mathematics'' §64): "
entity, an objector may urge, cannot be anything at all: two terms plainly are not identical, and one term cannot be, for what is it identical with?" Even before Russell,
Gottlob Frege
Friedrich Ludwig Gottlob Frege (; ; 8 November 1848 – 26 July 1925) was a German philosopher, logician, and mathematician. He was a mathematics professor at the University of Jena, and is understood by many to be the father of analytic ph ...
, at the beginning of "
On Sense and Reference," expressed a worry with regard to identity as a relation: "Equality gives rise to challenging questions which are not altogether easy to answer. Is it a relation?" More recently,
C. J. F. Williams
Christopher John Fardo Williams (31 December 1930 – 25 March 1997) was a British philosopher. His areas of interest were philosophical logic, on which topic he did most of his original work, and ancient philosophy, as an editor and translator. ...
has suggested that identity should be viewed as a second-order relation, rather than a relation between objects, and
Kai Wehmeier
Kai Frederick Wehmeier (born 1968) is a German-American philosopher and logician.
He is best known for proving that the fragment of Frege's inconsistent logical theory of ''Grundgesetze der Arithmetik'' becomes consistent upon restricting the ...
has argued that appealing to a binary relation that every object bears to itself, and to no others, is both logically unnecessary and metaphysically suspect.
Identity statements
Kind-terms, or
sortals
[Theodore Sider]
"Recent work on identity over time"
''Philosophical Books'' 41 (2000): 81–89. give a criterion of identity and non-identity among items of their kind.
See also
*
Counterpart theory
*
Difference (philosophy)
*
Exact similarity and identity
*
Four-dimensionalism/
perdurantism
*
Teleportation paradox
The teletransportation paradox or teletransport paradox (also known in alternative forms as the duplicates paradox) is a thought experiment on the philosophy of identity that challenges common intuitions on the nature of self and consciousness, ...
Notes
References
* 1998: ''Occasions of identity''. Oxford: Oxford University Press.
Google books* 1984: ''Reasons and persons''. Oxford: Oxford University Press.
Google books* 1985: Can amoebae divide without multiplying? ''Australasian journal of philosophy'', 63(3): 299–319.
* 2000:
eview of (1998) ''Philosophical review'', 109(3): 469–471
JSTOR* 2001:
eview of (1998) ''British journal for the philosophy science'', 52(2): 401–405.
External links
*Stanford Encyclopedia of Philosophy
Identity First published Wed 15 Dec 2004; substantive revision Sun 1 Oct 2006.
*Stanford Encyclopedia of Philosophy
Identity over time First published Fri 18 March 2005.
*Stanford Encyclopedia of Philosophy
Personal identity First published Tue 20 Aug 2002; substantive revision Tue 20 Feb 2007.
*Stanford Encyclopedia of Philosophy
Relative identity First published Mon 22 April 2002.
*
Fernando Andacht Fernando Torres Andacht is a Uruguayan-born semiotician.
Andacht studied Letters at the University of the Republic, graduating in 1978. Afterwards he obtained an MA in General Linguistics at Ohio University (1981), a Doctorate in Latin American Stu ...
, Mariela Michel,
A Semiotic Reflection on Selfinterpretation and Identity'.
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