Interpersonal Trust – Attempt of a Definition

Walter Bamberger, Technische Universität München, 2010

Trust is a term of everyday speech. Everyone knows it and has formed it during integration in her/his linguistic environment. In the end, the meaning of the term varies between individuals. In contrast, a scientific term needs a clearly delimited meaning and that meaning must be the same across all researchers. In addition, the term must describe something observable in order to represent a construct that is subject to investigations – as it is the case for interpersonal trust. These observable criteria constitute an operationalisation of the term, then.

In literature, many authors chose their own definition for trust. Often these definitions are no more than a limited operationalisation (Narowski, 1974). As a consequence, I define the term interpersonal trust in the following section as an attempt to integrate considerations from different authors. I invent no own definition, but mainly rely on Kassebaum’s (2004) definition.

I start the discussion of the term interpersonal trust (German: zwischenmenschliches Vertrauen or interpersonales Vertrauen) with a compact definition of Kassebaum. He integrated many definitions in literature as it incorporates the affective, behavioural, and cognitive component of trust; many authors considered only one or two of them (Narowski, 1974, p. 125). However, it is hardly possible to come to a common understanding of trust between you as the reader and me as the author within three sentences. For this reason, I highlight key aspects of the definition afterwards.

Interpersonal trust is an expectation about a future behaviour of another person and an accompanying feeling of calmness, confidence, and security depending on the degree of trust and the extend of the associated risk. That other person shall behave as agreed, unagreed but loyal, or at least according to subjective expectations, although she/he has the freedom and choice to act differently, because it is impossible or voluntarily unwanted to control her/him. That other person may also be perceived as a representative of a certain group. (Freely translated from Kassebaum, 2004, p. 21)

The Trusted Person

Interpersonal trust involves two parties who interact with each other: on the one hand side, the person who trusts, ego, the trustor (German: Vertrauender or Treugeber). In this report, I use the name Paula (P) for this person in many examples. On the other hand side, the person whom is trusted, alter, the trustee (German: Vertrauensperson or Treuhänder). I name this person Oliver (O). In the case that mutual trust develops over time in many interactions, both parties are ego and alter at the same time.

As part of the interaction, ego judges alter to be trustworthy or untrustworthy. Such a judgement about alter’s traits and motives is called attribution in social psychology. Studies have shown that the attribution process is very subjective. This is a basic finding that should be kept in mind when thinking about interpersonal trust.

The actor can perceive the other person as an individual or as a representative of a specific group. For example, one trusts a police man in a dangerous situation, because this person holds the role of a police man, but not because this person is trusted as a known and maybe familiar person (Strasser and Voswinkel, 1997). This kind of trust in the role of the other is called role trust (German: Rollenvertrauen) by Strasser and Voswinkel. In showing trust in the role, the trust in the abstract system of the police becomes practical. So, a person can have trust in the working of a system. Luhmann (1989, Chap. 7) calls this type of trust system trust (German: Systemvertrauen). This mechanism is important for a complex society with a high degree in the division of labour. Trust can be established between two persons, unfamiliar with each other, but acting on behalf of a trusted system. Gennerich (2000, pp. 40–44) extended this concept to general social groups to which a person can manifest a social identity. For example, fans in a soccer game form a community within that they trust each other to a certain extend. In contrast to system trust, Luhmann calls the trust in an individual – mostly based on familiarity – personal trust (German: persönliches Vertrauen).

Note: The object of trust can also be a thing or my self (self-confidence). These forms of trust are out of the scope of this report, as they are not referred to as interpersonal trust.

Direction to the Future

Burt and Knez chose “Trust is anticipated cooperation” (1995, p. 257) as a compact definition of interpersonal trust. Luhmann emphasises the anticipation of the future, as well: “Wer Vertrauen erweist, nimmt Zukunft vorweg. Er handelt so, als ob er der Zukunft sicher wäre” (1989, Chap. 2). The future consists of many possible scenarios; only one can become present – a process of complexity reduction. Someone who trusts, chooses from all the possibilities of future presents. With this choice, she/he simplifies her/his internal future.


Trust is a “middle state between knowing and not-knowing” about another person (Simmel, 1968, p. 263). Someone who knows everything about the specific problem to decide makes a rational decision and does not need to trust. Someone who knows nothing about the specific problem cannot trust but only hope. The trust decision forces the trustor to choose one out of the many possible scenarios the future offers (Luhmann, 1989, Chap. 2).

To meet the problem of the uncertainty, a probability could be estimated for each possible scenario. Trusting is an irrational process only partly based on clear evidence. It incorporates some rational decision calculus but deliberately goes beyond that (Strasser and Voswinkel, 1997). “es kommt durch Überziehen der vorhandenen Informationen zustande” (Luhmann, 1989, Chap. 4). Kee and Knox speak of a “subjective probability” and an inner, not rational “certainty or uncertainty about O’s trustworthiness” (1970, p. 359).

Expectation Towards the Other

Expectation is a belief that is associated with uncertainty and directed to the future. So, this term combines the previous two characteristics of trust. In addition, it specifies what to expect. “Vertrauen bezieht sich also stets auf eine kritische Alternative, [...]” (Luhmann, 1989, Chap. 4, p. 28).

Rempel et al. (1985) distinguish stages of trust that reflect different expectations towards the other: The most concrete stage is the partner’s predictability. It is mostly build from social learning experiences and, thus, refers to consistency and competence – it is trust in a behaviour of the other. The behaviour shall be right and loyal, or at least as expected (Strasser and Voswinkel, 1997). The second state, dependability, is about qualities and traits attributed to the other, for example, honesty, caring, and acceptance.

Luhmann restricts that not every expectation is trust-related. Expectations of trust are only those, “auf die hin man sich mit eigenem Handeln engagiert und bei deren Enttäuschung man das eigene Verhalten bereuen würde” (1989, Chap. 4, p. 29).


If the expectation is not fulfilled, harm is caused. The (subjective) value of the harm together with the (subjective) uncertainty reflects a risk. This risk is an immanent property of a trust situation.

Of what kind is the risked, often personal resource? It may be a material resource resulting in a direct financial harm, but also time, effort, and trouble. Rempel et al. give a couple of examples mostly relevant in intimate relationships: “[...] trust involves a willingness to put oneself at risk, be it through intimate disclosure, reliance on another’s promises, sacrificing present rewards for future gains, and so on” (1985, p. 96). In Gennerich’s model, trust always risks the own identity in some way. I detail this – in my opinion – interesting consideration in Section 1.2.

The harm arises if the other one acts untrustworthy. But if the other one fulfils the trust, one has a benefit from that. Examples for the benefit are future reciprocity in the relationship, health when going to the doctor, or a monetary benefit when accepting a “good deal”. The benefit is also associated with a subjective probability. Both together form a positive risk or chance. Luhmann (1989, Chap. 4) specifies that the perceived risk must be larger than the perceived chance in a trust situation. Otherwise the decision is more rational.

The risk is not only in the situation but also in the motives of the other. The trustor must decide whether the motives he perceives from the other are sufficient to trust in this situation. While Kee and Knox (1970) require that both sides must be cognisant of the risk for the trustor, Strasser and Voswinkel (1997) do not even postulate that the other must behave loyal. In their understanding, it is sufficient that an enemy or competitor behaves as expected. Then, the risk for the trustor may be hidden towards the other.

Voluntary or Forced Abandonment of Control

While both person should be interdependent in this situation, the trustee must still be free to some extend to behave trustworthy or untrustworthy (Kee and Knox, 1970). This freedom may be forced by the situation or voluntarily given by the trustor. From the point of view of the trusting person, it is a lack of control over situation that forces to trust.

For Luhmann, this is an important feature that characterises that kind of complexity the trust mechanism addresses: It is “jene Komplexität, die durch die Freiheit des anderen Menschen in die Welt kommt” (1989, p. 38).

The Affective, Behavioural, and Cognitive Component

Trust is an attitude towards the trust situation, including the trustee. Human beings can express an attitude, and hence trust, in three ways: with an affective, a behavioural, and a cognitive response (Fazio and Petty, 2008, pp. 7–11).

The affective response of trust consists of “feelings of confidence and security” (Rempel et al., 1985). The behavioural component can be formulated in a compact way as: “Trust is anticipated cooperation” (Burt and Knez, 1995). Within this component, trust is expressed as a verbal intention or as a behaviour with cooperative tendency. As the cognitive response, the individual thinks about the risk in the situation and the attributes of the other. The risk must be perceived cognisant, as Luhmann (1989, Chap. 4) and Kee and Knox (1970) emphasise.

Narowski (1974, pp. 125–130) points out, that the definitions in literature diverge, because they contain only few of these three responses. But, trust is reflected in all of them together.


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