1. Sociology

When it comes to trust, sociology is concerned with the position and role of trust in social systems. Interest in trust has grown significantly since the early eighties, from the early works of Luhmann,^[1] Barber^[2] and Giddens^[3] (see^[4] for a more detailed overview). This growth of interest in trust has been stimulated by on-going changes in society, characterised as late modernity and post-modernity.

Trust is one of several social constructs, an element of the social reality.^[5] It does not exist outside of our vision of the other. This image can be real or imaginary, but it is this one which permits the creation of the Trust.^[6] Other constructs, frequently discussed together with trust, are: control, confidence, risk, meaning and power. Trust is naturally attributable to relationships between social actors, both individuals and groups (social systems). Because trust is a social construct, it is valid to discuss whether trust can be trusted (e.g.^[7]), i.e. whether social trust operates as expected.

Society needs trust because it increasingly finds itself operating at the edge between confidence in what is known from everyday experience, and contingency of new possibilities. Without trust, all contingent possibilities should be always considered, leading to a paralysis of inaction.^[8] Trust can be seen as a bet on one of contingent futures, the one that may deliver benefits. Once the bet is decided (i.e. trust is granted), the trustor suspends his or her disbelief, and the possibility of a negative course of action is not considered at all. Because of it, trust acts as a reductor of social complexity, allowing for actions that are otherwise too complex to be considered (or even impossible to consider at all); specifically for cooperation.^[9] Sociology tends to focus on two distinct views: the macro view of social systems, and a micro view of individual social actors (where it borders with social psychology). Similarly, views on trust follow this dichotomy. Therefore, on one side the systemic role of trust can be discussed, with a certain disregard to the psychological complexity underpinning individual trust. The behavioural approach to trust is usually assumed^[10] while actions of social actors are measurable, leading to statistical modelling of trust. This systemic approach can be contrasted^[11] with studies on social actors and their decision-making process, in anticipation that understanding of such a process will explain (and allow to model) the emergence of trust.

Sociology acknowledges that the contingency of the future creates dependency between social actors, and specifically that the trustor becomes dependent on the trustee. Trust is seen as one of the possible methods to resolve such a dependency, being an attractive alternative to control.^[12] Trust is specifically valuable if the trustee is much more powerful than the trustor, yet the trustor is under social obligation to support the trustee.^[13]

Modern information technologies not only facilitated the transition towards post-modern society, but they also challenged traditional views on trust. Empirical studies^[14] confirms the new approach to the traditional question regarding whether technology artefacts can be attributed with trust. Trust is not attributable to artefacts, but it is a representation of trust in social actors such as designers, creators and operators of technology. Properties of technological artefacts form a message^[15] to determine trustworthiness of those agents.

The discussion about the impact of information technologies is still in progress. However, a conceptual re-thinking of technology-mediated social groups,^[16] or the proposition of a unifying socio-technical view on trust,^[17] from the perspective of social actors.

2. Psychology

In psychology, trust is believing that the person who is trusted will do what is expected. It starts at the family and grows to others. According to the psychoanalyst Erik Erikson development of basic trust is the first state psychosocial development occurring, or failing, during the first two years of life. Success results in feelings of security, trust, and optimism, while failure leads towards an orientation of insecurity and mistrust^[18] possibly resulting in attachment disorders.^[19]

A person's dispositional tendency to trust others can be considered a personality trait and as such is one of the strongest predictors of subjective well-being.^[20] It has been argued that trust increases subjective well-being because it enhances the quality of one's interpersonal relationships, and happy people are skilled at fostering good relationships.^[21]

Trust is integral to the idea of social influence: it is easier to influence or persuade someone who is trusting. The notion of trust is increasingly adopted to predict acceptance of behaviors by others, institutions (e.g. government agencies) and objects such as machines. However, once again perception of honesty, competence and value similarity (slightly similar to benevolence) are essential. There are three different forms of trust. Trust is being vulnerable to someone even when they are trustworthy; trustworthiness are the characteristics or behaviors of one person that inspire positive expectations in another person, and trust propensity being able to rely on people.^[22] Once trust is lost, by obvious violation of one of these three determinants, it is very hard to regain. Thus there is clear asymmetry in the building versus destruction of trust. Hence being and acting trustworthy should be considered the only sure way to maintain a trust level.

Increasingly much research has been done on the notion of trust and its social implications:

• Barbara Misztal, in her book,^[23] attempts to combine all notions of trust together. She points out three basic things that trust does in the lives of people: It makes social life predictable, it creates a sense of community, and it makes it easier for people to work together.
• In the context of sexual trust Riki Robbins^[24] describes four stages of trust.^[25]
• In the context of Information theory Ed Gerck defines and contrasts trust with social functions such as power, surveillance, and accountability.^[26][27]
• From a social identity perspective, the propensity to trust in strangers (see in-group favoritism) arises from the mutual knowledge of a shared group membership,^[28][29] stereotypes,^[29] or the need to maintain the group's positive distinctiveness.^[30]

In addition to the social influence, in organizational settings, trust may have a positive influence on the behaviors, perceptions, and performances of a person. Trust has a circular relationship with organizational justice perceptions such that perceived justice leads to trust which, in turn, promotes future perceptions of justice.^[31] One factor that enhances trust in a human being is facial resemblance. Through digital manipulation of facial resemblance in a two-person sequential trust game, supporting evidence was found that having similar facial features (facial resemblance) enhanced trust in a subject’s respective partner.^[32] Though facial resemblance was shown to increase trust, facial resemblance had the effect of decreased sexual desire in a particular partner. In a series of tests, digitally manipulated faces were presented to subjects to be evaluated for attractiveness within the context of a long term or short term relationship. The results showed that within the context of a short term relationship, which is dependent on sexual desire, similar facial features caused a decrease in said desire. Within the context of a long term relationship, which is dependent on trust, similar facial features increased the attractiveness of an individual, leading one to believe that facial resemblance and trust have great effects on relationships.^[33] Structure often creates trust in a person that encourages them to feel comfortable and excel in the workplace. Working anywhere may be stressful and takes effort. By having a conveniently organized area to work on, concentration will increase as well as effort. Structure is not just a method of order. It increases trust and therefore makes a workplace manageable. A structured, ordered environment produces trust as one may contain increased cooperation and perform on a higher level.

People may work together and achieve success through trust while working on projects that rely on each individual’s contribution.^[34]

Conversely, where trust is absent, projects can fail, especially if this lack of trust has not been identified and addressed. This is one facet of VPEC-T analysis: This thinking framework is used when studying information systems. Identifying and dealing with cases where information providers, information users, and those responsible for processing information do not trust one another can result in the removal of a risk factor for a project.

One's social relationship characterized by low trust and norms that discourage academic engagement are expected to be associated with low academic achievement. Individuals that are in relationships characterized by high levels of social trust are more apt to openly exchange information and to act with caring benevolence toward one another than those in relationships lacking trust.^[35]

An important key to treating sexual victimization of a child is the rebuilding of trust between parent and child. Failure for the adults to validate the sexual abuse contributes to the child's difficulty towards trusting self and others.^[36] Trust is often affected by the erosion of a marriage. Children of divorce do not exhibit less trust in mothers, partners, spouses, friends, and associates than their peers of intact families. The impact of parental divorce is limited to trust in the father.^[37]

2.1. Social Identity Approach

The social identity approach explains trust in strangers as a function of group-based stereotypes or in-group favouring behaviours based on salient group memberships. With regard to ingroup favoritism, people generally think well of strangers but expect better treatment from in-group members in comparison to out-group members. This greater expectation then translates into a higher propensity to trust an in-group rather than out-group member.^[28][30][38] It has been pointed out that it is only advantageous to form such expectations of an in-group stranger if they too know the group membership of the recipient.^[38]

There is considerable empirical activity related to the social identity approach. Allocator studies have frequently been employed to understand group-based trust in strangers.^{[28][29][38][39]} They may be operationalised as unilateral or bilateral relationships of exchange. General social categories such as university affiliation, course majors, and even ad-hoc groups have been used to distinguish between in-group and out-group members. In unilateral studies of trust, the participant would be asked to choose between envelopes containing money that was previously allocated by an in-group or out-group member.^[38] They would have had no prior or future opportunities for interaction, simulating Brewer’s notion that group membership was sufficient in bringing about group-based trust and hence cooperation.^[40] Participants could expect an amount ranging from nothing to the maximum value an allocator could give out. In bilateral studies of trust have employed an investment game devised by Berg and colleagues where individuals could choose to give a portion or none of their money to another.^[41] Any amount given would be tripled and the receiver would then decide on whether they would return the favour by giving money back to the sender. Trusting behaviour on the part of the sender and the eventual trustworthiness of the receiver was exemplified through the giving of money.^[30][38]

The above empirical research has demonstrated that when group membership is made salient and known to both parties, trust is granted more readily to in-group members than out-group members.^[29][38][39] This occurred even when the in-group stereotype was comparatively less positive than an out-group’s (e.g. psychology versus nursing majors),^[29] in the absence of personal identity cues,^[30] and when participants had the option of a sure sum of money (i.e. in essence opting out of the need to trust a stranger).^[28] In contrast, when only the recipient was made aware of group membership trust becomes reliant upon group stereotypes.^[29][30] The group with the more positive stereotype was trusted (e.g. one’s university affiliation over another),^[30] even over that of the in-group (e.g. nursing over psychology majors).^[29] Another reason for in-group favouring behaviours in trust could be attributed to the need to maintain in-group positive distinctiveness, particularly in the presence of social identity threat.^[39] It should also be noted that trust in out-group strangers increased when personal cues to identity were revealed.^[30]

3. Philosophy

Some philosophers argue that trust is more than a relationship of reliance. Philosophers such as Annette Baier have made a difference between trust and reliance by saying that trust can be betrayed, whilst reliance can only be disappointed (Baier 1986, 235).^[42] Carolyn McLeod explains Baier's argument by giving the following examples: we can rely on our clock to give the time, but we do not feel betrayed when it breaks, thus, we cannot say that we trusted it; we are not trusting when we are suspicious of the other person, because this is in fact an expression of distrust (McLeod 2006).^[43] Thus, trust is different from reliance in the sense that a truster accepts the risk of being betrayed.

The definition of trust as a belief in something or a confident expectation about something^[44] leads to eliminate the notion of risk from the definition, because it does not include whether the expectation or belief is favorable or unfavorable. For example, to have an expectation of a friend arriving to dinner late because she has habitually arrived late for the last fifteen years, is a confident expectation (whether or not we agree with her annoying late arrivals.) The trust is not about what we wish for, rather it is in the consistency of the data of our habits. As a result, there is no risk or betrayal because the data now exists as collective knowledge.

4. Economics

Trust in economics is treated as an explanation for a difference between actual human behaviour and the one that can be explained by the individual desire to maximize one's utility. In economic terms, trust can provide an explanation of a difference between Nash equilibrium and the observed equilibrium. Such an approach can be applied to individuals as well as societies.

Trust is also seen as an economic lubricant, reducing the cost of transactions between parties, enabling new forms of cooperation and generally furthering business activities;^[45][46] employment and prosperity. This observation ^[47] created a significant interest in considering trust as a form of social capital and has led research into closer understanding of the process of creation and distribution of such capital. It has been claimed that higher level of social trust is positively correlated with economic development. Even though the original concept of 'high trust' and 'low trust' societies may not necessarily hold, it has been widely accepted and demonstrated that social trust benefits the economy ^[48] and that a low level of trust inhibits economic growth.

Theoretical economical modelling ^[49] demonstrated that the optimum level of trust that a rational economic agent should exhibit in transactions is equal to trustworthiness of the other party. Such a level of trust leads to efficient market. Trusting less lead to the loss of economic opportunities, trusting more leads to unnecessary vulnerabilities and potential exploitation.

Economics is also interested in quantifying trust, usually in monetary terms. The level of correlation between increase in profit margin ^[50] or decrease in transactional cost can be used as indicators of economic value of trust.

Economic 'trust games' are popularly used to empirically quantify trust in relationships under laboratory conditions. There are several games and game-like scenarios related to trust that have been tried, with certain preferences to those that allow to estimate confidence in monetary terms.^[51] Games of trust are designed in a way that their Nash equilibrium differ from Pareto optimum so that no player alone can maximise his own utility by altering his selfish strategy without cooperation while cooperating partners can benefit.

The classical version of the game of trust has been described in ^[52] as an abstracted investment game, using the scenario of an investor and a broker. Investor can invest a fraction of his money, and broker can return only part of his gains. If both players follow their economical best interest, the investor should never invest and the broker will never be able to re-pay anything. Thus the flow of money flow, its volume and character is attributable entirely to the existence of trust.

The game can be played as one-off, or as a repetitive one, between the same or different sets of players, to distinguish between a general propensity to trust and trust within particular relationships. Several other variants of this game exist. Reversing rules lead to the game of distrust, pre-declarations can be used to establish intentions of players,^[53] while alterations to the distribution of gains can be used to manipulate perception of both players. The game can be also played by several players on the closed market,^[54] with or without information about reputation.

Other interesting games are e.g. binary-choice trust games,^[55] the gift-exchange game ^[56] and various other forms of social games. Specifically games based on the Prisoner's Dilemma ^[57] are popularly used to link trust with economic utility and demonstrate the rationality behind reciprocity.

The work of Rachel Botsman is also very important about collaboration economy.

The popularisation of e-commerce opened the discussion of trust in economy to new challenges while at the same time elevating the importance of trust, and desire to understand customer decision to trust.^[58] For example, inter-personal relationship between the buyer and the seller has been dis-intermediated by the technology,^[59] and had to be improved upon.^[60] Alternatively, web sites could be made to convince the buyer to trust the seller, regardless of seller's actual trustworthiness (e.g.^[61]) . Reputation-based systems improved on trust assessment by allowing to capture the collective perception of trustworthiness, generating significant interest in various models of reputation.^[62]

5. Systems

In systems, a trusted component has a set of properties which another component can rely on. If A trusts B, this means that a violation in those properties of B might compromise the correct operation of A. Observe that those properties of B trusted by A might not correspond quantitatively or qualitatively to B’s actual properties. This happens when the designer of the overall system does not take the relation into account. In consequence, trust should be placed to the extent of the component’s trustworthiness. The trustworthiness of a component is thus, not surprisingly, defined by how well it secures a set of functional and non-functional properties, deriving from its architecture, construction, and environment, and evaluated as appropriate.^[63]