Rationality is the quality or state of being rational, i.e. agreeable to reason. Rationality implies the conformity of a person’s beliefs with their reasons to believe and of their actions with their reasons for action. When a goal or problem requires making a decision, rationality factors in all information that is available (e.g. complete or incomplete knowledge).
It is meaningless to assert rationality without also specifying the background model assumptions describing how the problem is framed and formulated. Rationality is relative: in models that optimize for personal benefit, self-interested or even selfish behavior is rational; in models that favor benefiting the group over the individual, purely selfish behavior is deemed irrational.
German sociologist Max Weber proposed an interpretation of social action that distinguished between four different idealized types of rationality. The first, which he called ‘Zweckrational’ or ‘purposive/instrumental’ rationality, is related to expectations about the behavior of other human beings or objects in the environment. These expectations serve as means for a particular actor to attain ends, ends which Weber noted were ‘rationally pursued and calculated.’ The second type, Weber called ‘Wertrational’ or ‘value/belief-oriented.’ Here the action is undertaken for what one might call reasons intrinsic to the actor: some ethical, aesthetic, religious or other motive, independent of whether it will lead to success.
The third type was ‘affectual,’ determined by an actor’s specific affect, feeling, or emotion—to which Weber himself said that this was a kind of rationality that was on the borderline of what he considered ‘meaningfully oriented.’ The fourth was traditional or conventional, determined by ingrained habituation. Weber emphasized that it was very unusual to find only one of these orientations: combinations were the norm. His usage also makes clear that he considered the first two as more significant than the others, and it is arguable that the third and fourth are subtypes of the first two.
The advantage in Weber’s interpretation of rationality is that it avoids a value-laden assessment, say, that certain kinds of beliefs are irrational. Instead, Weber suggests that a ground or motive can be given—for religious or affect reasons, for example—that may meet the criterion of explanation or justification even if it is not an explanation that fits the purposive/instrumental Zweckrational orientation of means and ends. The opposite is therefore also true: some means-ends explanations will not satisfy those whose grounds for action are value/belief-oriented Wertrational type.
In the psychology of reasoning, psychologists and cognitive scientists have defended different positions on human rationality. One prominent view, stemming from psychologist Philip Johnson-Laird and cognitive scientist Ruth M. J. Byrne, is that humans are rational in principle but err in practice, that is, humans have the competence to be rational but their performance is limited by various factors. However, it has been argued that many standard tests of reasoning suffer from methodological and conceptual problems. This has led to disputes in psychology over whether researchers should only use standard rules of logic, probability theory, and statistics, or rational choice theory as norms of good reasoning.
Opponents of this view, such as German psychologist Gerd Gigerenzer, favor a conception of bounded rationality, especially for tasks under high uncertainty. Bounded rationality is the idea that rationality is limited, when individuals make decisions, by the tractability of the decision problem, the cognitive limitations of the mind, and the time available to make the decision. Decision-makers, in this view, act as satisficers, seeking a satisfactory solution rather than an optimal one.
Rationality theorist Jesús Mosterín makes a parallel distinction between theoretical and practical rationality, although, according to him, reason and rationality are not the same: reason would be a psychological faculty, whereas rationality is an optimizing strategy. Humans are not rational by definition, but they can think and behave rationally or not, depending on whether they apply, explicitly or implicitly, the strategy of theoretical and practical rationality to the thoughts they accept and to the actions they perform. Mosterín also distinguishes between involuntary and implicit belief, on the one hand, and voluntary and explicit acceptance, on the other. Theoretical rationality can more properly be said to regulate our acceptances than our beliefs. Practical rationality is the strategy for living one’s best possible life, achieving your most important goals and your own preferences in as far as possible.
As the study of arguments that are correct in virtue of their form, logic is of fundamental importance in the study of rationality. The study of rationality in logic is more concerned with epistemic rationality, that is, attaining beliefs in a rational manner, than instrumental rationality (pursuit by any means necessary to achieve a specific end).
Rationality also plays a key role in economics. For example, the economic concept of ‘instrumentality’ assumes that people and organizations are instrumentally rational (i.e. adopt the best actions to achieve their goals). Also, an axiom of economics holds that rationality is a matter of being logically consistent within your preferences and beliefs. Economic rationality also considers accuracy of beliefs and full use of information—in this view a person who is not rational has beliefs that don’t fully use the information they have.
Critics argue that economic rational choice theory is a useless concept for understanding human behavior; the term ‘homo economicus’ (economic man: the imaginary man being assumed in economic models who is logically consistent but amoral) was coined largely in honor of this view. Behavioral economics aims to account for economic actors as they actually are, allowing for psychological biases, rather than assuming idealized instrumental rationality.
Within artificial intelligence, a rational agent is typically one that maximizes its expected utility, given its current knowledge. Utility is the usefulness of the consequences of its actions. The utility function is arbitrarily defined by the designer, but should be a function of ‘performance,’ which is the directly measurable consequences, such as winning or losing money. In order to make a safe agent that plays defensively, a nonlinear function of performance is often desired, so that the reward for winning is lower than the punishment for losing. An agent might be rational within its own problem area, but finding the rational decision for arbitrarily complex problems is not practically possible. The rationality of human thought is a key problem in the psychology of reasoning.
The Daily Omnivore 
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