What is "reciprocity"

Reciprocity \Rec`i*proc"i*ty\ (r[e^]s`[i^]*pr[o^]s"[i^]*t[y^]), n. [Cf. F. r['e]ciprocit['e]. See Reciprocal.]

1. Mutual action and reaction.

2. Reciprocal advantages, obligations, or rights; reciprocation.

   Reciprocity treaty, or Treaty of reciprocity, a treaty concluded between two countries, conferring equal privileges as regards customs or charges on imports, or in other respects.

   Syn: Reciprocation; interchange; mutuality.

1766, from French réciprocité (18c.), from reciproque, from Latin reciprocus, past participle of reciprocare (see reciprocal).

n. 1 The characteristic of being reciprocal, e.g. of a relationship between people. 2 A reciprocal relationship. 3 A relation of mutual dependence or action or influence. 4 The mutual exchange of rights, privileges or obligations between nations. 5 (context psychology English) The responses of individuals to the actions of others.

1. n. a relation of mutual dependence or action or influence [syn: reciprocality]

2. mutual exchange of commercial or other privileges

Reciprocity may refer to:

• Reciprocity (Canadian politics), free trade with the United States of America
  • Reciprocal trade agreement, entered into in order to reduce (or eliminate) tariffs, quotas and other trade restrictions on items traded between the signatories
• Reciprocity (photography), the relationship between the intensity of the light and duration of the exposure that result in identical exposure
• Traffic violations reciprocity where non-resident drivers are treated like residents
• Reciprocity (Fringe), a 2011 episode of the television series Fringe
• Quid pro quo, a legal concept of the exchange of good or services, each having value

In international relations and treaties, the principle of reciprocity states that favours, benefits, or penalties that are granted by one state to the citizens or legal entities of another, should be returned in kind.

For example, reciprocity has been used in the reduction of tariffs, the grant of copyrights to foreign authors, the mutual recognition and enforcement of judgments, and the relaxation of travel restrictions and visa requirements.

The principle of reciprocity also governs agreements on extradition.

Reciprocity, in 19th- and early 20th-century Canadian politics, meant free trade, the removal of protective tariffs on all natural resources, between Canada and the United States. Reciprocity and free trade have been emotional issues in Canadian history, as they pitted two conflicting impulses: the desire for beneficial economic ties with the United States and the fear of closer economic ties leading to American domination and even annexation.

In cultural anthropology, reciprocity refers to the non-market exchange of goods or labour ranging from direct barter (immediate exchange) to forms of gift exchange where a return is eventually expected (delayed exchange) as in the exchange of birthday gifts. It is thus distinct from the true gift, where no return is expected. Reciprocity is said to be the basis of most non-market exchange. David Graeber argues, "as currently used, 'reciprocity' can mean almost anything. It is very close to meaningless."

When the exchange is immediate, as in barter, it does not create a social relationship. When the exchange is delayed, it creates both a relationship as well as an obligation for a return (i.e. debt). Hence, some forms of reciprocity can establish hierarchy if the debt is not repaid. The failure to make a return may end a relationship between equals. Reciprocal exchanges can also have a political effect through the creation of multiple obligations and the establishment of leadership, as in the gift exchanges (Moka) between Big Men in Melanesia. Some forms of reciprocity are thus closely related to redistribution, where goods and services are collected by a central figure for eventual distribution to followers.

Marshall Sahlins, a well-known American cultural anthropologist, identified three main types of reciprocity (generalized, balanced and negative) in the book Stone Age Economics (1972). Reciprocity was also the general principal used by Claude Lévi-Strauss to explain the Elementary Structures of Kinship (1949), in one of the most influential works on kinship theory in the post-war period.

In network science, reciprocity is a measure of the likelihood of vertices in a directed network to be mutually linked. Like the clustering coefficient, scale-free degree distribution, or community structure, reciprocity is a quantitative measure used to study complex networks.

Reciprocity in evolutionary biology refers to mechanisms whereby the evolution of cooperative or altruistic behaviour may be favoured by the probability of future mutual interactions. A corollary is how a desire for revenge can harm the collective and therefore be naturally deselected.

In photography reciprocity is the inverse relationship between the intensity and duration of light that determines the reaction of light-sensitive material. Within a normal exposure range for film stock, for example, the reciprocity law states that the film response will be determined by the total exposure, defined as intensity × time. Therefore, the same response (for example, the optical density of the developed film) can result from reducing duration and increasing light intensity, and vice versa.

The reciprocal relationship is assumed in most sensitometry, for example when measuring a Hurter and Driffield curve (optical density versus logarithm of total exposure) for a photographic emulsion. Total exposure of the film or sensor, the product of focal-plane illuminance times exposure time, is measured in lux seconds.

In social psychology, reciprocity is a social rule that says people should repay, in kind, what another person has provided for them; that is, people give back (reciprocate) the kind of treatment they have received from another. By virtue of the rule of reciprocity, people are obligated to repay favors, gifts, invitations, etc. in the future. If someone receives a gift for their birthday, a reciprocal expectation may influence them to do the same on the gift-giver's birthday. This sense of future obligation associated with reciprocity makes it possible to build continuing relationships and exchanges. Reciprocal actions of this nature are important to social psychology as they can help explain the maintenance of social norms.

A person who violates the reciprocity norm by accepting without attempting to return the good acts of others is disliked by the social group. Individuals who benefit from the group's resources without contributing any skills, helping, or resources of their own are called free riders. Both individuals and social groups often punish free riders, even when this punishment results in considerable costs to the group. Therefore, it is unsurprising that individuals will go to great lengths to avoid being seen as a moocher, freeloader, or ingrate.

Reciprocal actions differ from altruistic actions in that reciprocal actions only follow from others' initial actions, while altruism is the act of social gift-giving without hope or expectation of future positive responses. Some distinguish between ideal altruism (giving with no expectation of future reward) and reciprocal altruism (giving with expectation of future reward). For more information on this idea, see altruism or altruism (ethics).

The social norm of reciprocity is the expectation that people will respond to each other in similar ways—responding to gifts and kindnesses from others with similar benevolence of their own, and responding to harmful, hurtful acts from others with either indifference or some form of retaliation. Such norms can be crude and mechanical, such as a literal reading of the eye-for-an-eye rule lex talionis, or they can be complex and sophisticated, such as a subtle understanding of how anonymous donations to an international organization can be a form of reciprocity for the receipt of very personal benefits, such as the love of a parent.

The norm of reciprocity varies widely in its details from situation to situation, and from society to society. Anthropologists and sociologists have often claimed, however, that having some version of the norm appears to be a social inevitability. Reciprocity figures prominently in social exchange theory, evolutionary psychology, social psychology, cultural anthropology and rational choice theory.

Reciprocity in linear systems is the principle that a response Rab, measured at a location (and direction if applicable) a, when the system has an excitation signal applied at a location (and direction if applicable) b, is exactly equal to Rba which is the response at location b, when that same excitation is applied at a. This applies for all frequencies of the excitation signal. If Hab is the transfer function between a and b then Hab = Hba, if the system is linear.

In the special case of a modal analysis this is known as Maxwell's reciprocity theorem.

The reciprocity principle is also used in the analysis of structures. When combined with superposition, symmetry and anti-symmetry, it can be used to resolve complex load conditions.

In classical electromagnetism, reciprocity refers to a variety of related theorems involving the interchange of time- harmonic electric current densities (sources) and the resulting electromagnetic fields in Maxwell's equations for time-invariant linear media under certain constraints. Reciprocity is closely related to the concept of Hermitian operators from linear algebra, applied to electromagnetism.

Perhaps the most common and general such theorem is Lorentz reciprocity (and its various special cases such as Rayleigh-Carson reciprocity), named after work by Hendrik Lorentz in 1896 following analogous results regarding sound by Lord Rayleigh and light by Helmholtz (Potton, 2004). Loosely, it states that the relationship between an oscillating current and the resulting electric field is unchanged if one interchanges the points where the current is placed and where the field is measured. For the specific case of an electrical network, it is sometimes phrased as the statement that voltages and currents at different points in the network can be interchanged. More technically, it follows that the mutual impedance of a first circuit due to a second is the same as the mutual impedance of the second circuit due to the first.

Reciprocity is useful in optics, which (apart from quantum effects) can be expressed in terms of classical electromagnetism, but also in terms of radiometry.

There is also an analogous theorem in electrostatics, known as Green's reciprocity, relating the interchange of electric potential and electric charge density.

Forms of the reciprocity theorems are used in many electromagnetic applications, such as analyzing electrical networks and antenna systems. For example, reciprocity implies that antennas work equally well as transmitters or receivers, and specifically that an antenna's radiation and receiving patterns are identical. Reciprocity is also a basic lemma that is used to prove other theorems about electromagnetic systems, such as the symmetry of the impedance matrix and scattering matrix, symmetries of Green's functions for use in boundary-element and transfer-matrix computational methods, as well as orthogonality properties of harmonic modes in waveguide systems (as an alternative to proving those properties directly from the symmetries of the eigen-operators).

"Reciprocity" is the eleventh episode of the third season of the American science fiction drama television series Fringe, and the 54th episode overall. In the episode, the Fringe division follows a chain of shapeshifter murders as the assembly of the doomsday device nears completion. Ryan McDonald and Charles Parnell guest starred.

Co-executive producer Josh Singer wrote "Reciprocity", his seventh such credit for the series. For his third Fringe directional credit, Jeannot Szwarc served as the director. The episode first aired in the United States on January 28, 2011 to an estimated 4.57 million viewers, making it the highest rated program of the night. Television critics generally viewed the episode positively, with a number praising the reveal of the shapeshifter killer's identity.