Agents

Agents in Promise Theory are said to be autonomous, meaning that they are causally independent of one another. This independence implies that they cannot be controlled from without, they originate their own behaviours entirely from within, yet they can rely on one another's services through the making of promises to signal cooperation. Agents are thus self-determined until such a time as they partially or completely give up their independence by promising to accept guidance from other agents.^{[citation needed]}

Agents may be very simple, like a heading in a HTML document, or very complex, like a name server in a network e.g. a DNS server. Regardless of internal complexity, and agent embody mechanisms in order to keep promises. A HTML heading makes promises about its own rendering via CSS statements.^[26] A DNS server promises to answer requests for addresses given a name.^[14] The first extremely simple, the latter much more sophisticated. These differences in internal process complexity lead to a definition of so-called ‘semantic scaling' of agent complexity.

Intentions and outcomes

Agents in Promise Theory may have `intentions'. An intention may be realized by a behaviour or a target outcome. Intentions are thus made concrete by defining a set of acceptable outcomes associated with each intention. An outcome is most useful when it describes an invariant or mathematical fixed point in some description of states, because this can be both dynamically and semantically stable.

Each intention expresses a quantifiable outcome, which may be described as a state of an agent. Intentions are sometimes described as targets, goals, or desired states. The selection of intentions by an agent is left unexplained so as to avoid questions about free will.^[1]

Agents express their intentions to one another by 'promise' or by 'imposition'. This provides a measure by which they can 'assess' whether intentions are fulfilled or not (i.e. whether promises are kept).^{[citation needed]}

Promises

Promises arise when an agent shares one of its intentions with another agent voluntarily, e.g. by publishing its intent. The method of sharing is left to the modeller to explain.

For example, an object, such as a door handle, is an agent that promises to be suitable for opening a door, although it could be used for something else, e.g. for digging a hole in the ground. We cannot assume that agents will accept the promises given in the spirit in which they were intended, because every agent has its own context and capabilities. The promise of 'door handleness' could be expressed by virtue of its physical form or by having a written label attached in some language. An agent that uses this promise can assess whether the agent keeps its promise, or is 'fit for purpose'. Any agent can decide this for itself.

A promise may be used voluntarily by another agent in order to influence its usage of the other agent. Promises facilitate interaction, cooperation, and tend to maximize an intended outcome. Promises are not commands or deterministic controls.^{[citation needed]}

Autonomy

Obligations, rather than promises have been the traditional way of modelling behaviour - in society, in technology and other areas.^[27] While still dominant, the obligation based model has known weaknesses, in particular in areas like scalability and predictability, because of its rigidness and lack of dynamism.

Promise Theory's point of departure from obligation logics is the idea that all agents in a system should have autonomy of control—i.e. that they cannot be coerced or forced into a specific behaviour. Obligation theories in computer science often view an obligation as a deterministic command that causes its proposed outcome. In Promise Theory an agent may only make promises about its own behaviour. For autonomous agents it is meaningless to make promises about another's behaviour.

Although this assumption could be interpreted morally or ethically, in Promise Theory this is simply a pragmatic `engineering' principle, which leads to a more complete declaration of the intended roles of the actors or agents in a system: When making assumptions about others' behaviour is disallowed, one is forced to document every promise more completely in order to make predictions which in turn will reveal possible failure modes by which cooperative behaviour could fail.

Command and control systems like those that motivate obligation theories can easily be reproduced by having agents voluntarily promise to follow the instructions of another agent (this is also viewed as a more realistic model of behaviour). Since a promise can always be withdrawn, there is no contradiction between voluntary cooperation and command and control.

In Philosophy and Law a promise is often viewed as something that leads to an obligation. Promise Theory rejects that point of view. Bergstra and Burgess state that the concept of a promise is quite independent of that of obligation.^[27]

Economics

Promises can be valuable to the promisee or even to the promiser. They might also lead to costs. There is thus an economic story to tell about promises. The economics of promises naturally motivate `selfish agent' behaviour and Promise Theory can be seen as a motivation for game theoretical decision making, in which multiple promises play the role of strategies in a game.^[28]

Promise Theory has also been used to model and build new insights into monetary systems.^[6]