Trust is a relationship of reliance. A trusted party is presumed to seek to fulfill policies, ethical codes, law and their previous promises.

Trust does not need to involve belief in the good character, vices, or morals of the other party. Persons engaged in a criminal activity usually trust each other to some extent. Also, trust does not need to include an action that you and the other party are mutually engaged in. Trust is a prediction of reliance on an action, based on what a party knows about the other party. Trust is a statement about what is otherwise unknown -- for example, because it is far away, cannot be verified, or is in the future.

Sociology

In the social sciences, the subtleties of trust are a subject of ongoing research. In sociology (and psychology) the degree to which one party trusts another is a measure of belief in the honesty, benevolence and competence of the other party. Based on the most recent research, a failure in trust may be forgiven more easily if it is interpreted as a failure of competence rather than a lack of benevolence or honesty.

From this perspective, trust is a mental state, which cannot be measured directly. Confidence in the results of trusting may be measured through behavior, or alternatively, one can measure self-reported trust (with all the caveat surrounding that method). Trust may be considered a moral choiceFact: date=April 2007, or at least a heuristic, allowing the human to deal with complexities that outgo rationalistic reasoning. In this case, machine-human trust is meaningless, because computers have no moral sense and rely on rational computations. Any trust in a device under this characterization is computer-mediated trust of the user of the machine in the designer and creator of the device; who has implemented the rational rules into the device. Francis Fukuyama and Tyler are academics who advocate this conception of trust – as moral and not directly observable.

A second perspective in social theory comes from the classic Foundations of Social Theory by James S. Coleman. Coleman offers a four-part definition:

1. Placement of trust allows actions that otherwise are not possible (i.e. trust allows actions to be conducted based on incomplete information on the case in hand).
2. The person in whom trust is placed (trustee) is trustworthy, then the trustor will be better off than if he or she had not trusted. Conversely, if the trustee is not trustworthy, then the trustor will be worse off than if he or she had not trusted (this is reminiscent of a classical prisoner's dilemma).
3. Trust is an action that involves a voluntary transfer of resources (physical, financial, intellectual, or temporal) from the truster to the trustee with no real commitment from the trustee (again prisoner's dilemma).
4. A time lag exists between the extension of trust and the result of the trusting behavior.