Cooperation and sincerity

In all of the examples presented in this thesis, the agents use a shared utility function, since the computer acts as a fully cooperative assistant to the user and so holds the same preferences over outcomes. This guarantees that acts are recognised as having sincere intent. For example, an informing act whose precondition is that the speaker believes the told proposition would not usually be chosen if the precondition failed. If it were to be chosen, it would lead the hearer to a state of false belief, which would lead him to choose an irrelevant and therefore usually worse strategy. Since the utility function is shared, this would also be a worse strategy for the speaker. There are devices such as the "white lie", where the false belief happens to lead the hearer to a better strategy. For instance, saying it is cold when it is not is a good way to get someone to close the window. White lies should be plannable in the system, by means of a sincere and an insincere version of the plan rule for the informing act. However, regarding acts as being sincere reduces the number of hypotheses that the hearer must entertain about the speaker's intent, thus reducing the breadth of the game tree without reducing the abilities of the system for any of the problems explored in this thesis.

It is not difficult to generalise the system to be used for problems in which agents are self-interested rather than fully cooperative. It only requires that each agent is given its own utility function, and that agents are allowed to make choices that are insincere by dropping the belief preconditions. One specialisation of this is the zero-sum game, in which the utility functions of each agent sum to zero. In this instance, it turns out that while the agents must choose some act, it is never of benefit to choose a spoken act. This is because a spoken act would do nothing but reveal the agent's mental state, which would if anything be advantageous to the opponent, and so with opposing utility functions, a disadvantage to the speaker. Such behaviour can be found in games such as poker, where players must act by moving cards, but minimise any other acts that would reveal something about their mental state.