  The concept of rationality is central to the field of artificial
intelligence. Whether we are seeking to simulate human reasoning, or the goal
is to achieve bounded optimality, we generally seek to make artificial agents
as rational as possible. Despite the centrality of the concept within AI, there
is no unified definition of what constitutes a rational agent. This article
provides a survey of rationality and irrationality in artificial intelligence,
and sets out the open questions in this area. The understanding of rationality
in other fields has influenced its conception within artificial intelligence,
in particular work in economics, philosophy and psychology. Focusing on the
behaviour of artificial agents, we consider irrational behaviours that can
prove to be optimal in certain scenarios. Some methods have been developed to
deal with irrational agents, both in terms of identification and interaction,
however work in this area remains limited. Methods that have up to now been
developed for other purposes, namely adversarial scenarios, may be adapted to
suit interactions with artificial agents. We further discuss the interplay
between human and artificial agents, and the role that rationality plays within
this interaction; many questions remain in this area, relating to potentially
irrational behaviour of both humans and artificial agents.
