School

Rationality

Overview

Rationality is the quality of being guided by or based on reason. In this regard, a person acts rationally if they have a good reason for what they do, or a belief is rational if it is based on strong evidence. This quality can apply to an ability, as in a rational animal, to a psychological process, like reasoning, to mental states, such as beliefs and intentions, or to persons who possess these other forms of rationality. A thing that lacks rationality is either arational, if it is outside the domain of rational evaluation, or irrational, if it belongs to this domain but does not fulfill its standards.

There are many discussions about the essential features shared by all forms, or accounts, of rationality. According to reason-responsiveness accounts, to be rational is to be responsive to reasons. For example, dark clouds are a reason for taking an umbrella, which is why it is rational for an agent to do so in response. An important rival to this approach are coherence-based accounts, which define rationality as internal coherence among the agent's mental states. Many rules of coherence have been suggested in this regard, for example, that one should not hold contradictory beliefs or that one should intend to do something if one believes that one should do it.

Goal-based accounts characterize rationality in relation to goals, such as acquiring truth in the case of theoretical rationality. Internalists believe that rationality depends only on the person's mind. Externalists contend that external factors may also be relevant. Debates about the normativity of rationality concern the question of whether one should always be rational. A further discussion is whether rationality requires that all beliefs be reviewed from scratch rather than trusting pre-existing beliefs.

Various types of rationality are discussed in the academic literature. The most influential distinction is between theoretical and practical rationality. Theoretical rationality concerns the rationality of beliefs. Rational beliefs are based on evidence that supports them. Practical rationality pertains primarily to actions. This includes certain mental states and events preceding actions, like intentions and decisions. In some cases, the two can conflict, as when practical rationality requires that one adopts an irrational belief. Another distinction is between ideal rationality, which demands that rational agents obey all the laws and implications of logic, and bounded rationality, which takes into account that this is not always possible since the computational power of the human mind is too limited. Most academic discussions focus on the rationality of individuals. This contrasts with social or collective rationality, which pertains to collectives and their group beliefs and decisions.

Rationality is important for solving all kinds of problems in order to efficiently reach one's goal. It is relevant to and discussed in many disciplines. In ethics, one question is whether one can be rational without being moral at the same time. Psychology is interested in how psychological processes implement rationality. This also includes the study of failures to do so, as in the case of cognitive biases. Cognitive and behavioral sciences usually assume that people are rational enough to predict how they think and act. Logic studies the laws of correct arguments. These laws are highly relevant to the rationality of beliefs. A very influential conception of practical rationality is given in decision theory, which states that a decision is rational if the chosen option has the highest expected utility. Other relevant fields include game theory, Bayesianism, economics, and artificial intelligence.

Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).

In the original texts

Passages from public-domain books where Rationality is discussed.

Albeit the absolute is defined as being necessarily an embodiment of objectively perfect rationality, it is fair to its english advocates to say that those who have espoused the hypothesis most concretely and seriously have usually avowed the irrationality to their own minds of certain elements in it.
William James, A Pluralistic Universe
names the idea; states what it is; opens on it
Read the chapter · Open in the reader
There is nothing irrational in the passions as such, and many irrational people feel only the most trivial passions. No man need fear that by making himself rational he will make his life dull. On the contrary, since rationality consists in the main of internal harmony, the man who achieves it is freer in his contemplation of the world and in the use of his energies to achieve external purposes than is the man who…
Bertrand Russell, The conquest of happiness
states what it is; names the idea; opens on it
Read the chapter · Open in the reader
In this way a world of rational beings (mundus intelligibilis) is possible as a kingdom of ends, and this by virtue of the legislation proper to all persons as members. Therefore every rational being must so act as if he were by his maxims in every case a legislating member in the universal kingdom of ends. The formal principle of these maxims is: "So act as if thy maxim were to serve likewise as the universal law…
Immanuel Kant, Fundamental Principles of the Metaphysic of Morals
states what it is; author linked in the graph
Read the chapter · Open in the reader
Philosophers long ago observed the remarkable fact that mere familiarity with things is able to produce a feeling of their rationality. The empiricist school has been so much struck by this circumstance {77} as to have laid it down that the feeling of rationality and the feeling of familiarity are one and the same thing, and that no other kind of rationality than this exists. The daily contemplation of phenomena…
William James, The Will to Believe, and Other Essays in Popular Philosophy
names the idea; opens on it
Read the chapter · Open in the reader
But all philosophy is either cognition on the basis of pure reason, or the cognition of reason on the basis of empirical principles. The former is termed pure, the latter empirical philosophy. The philosophy of pure reason is either propædeutic, that is, an inquiry into the powers of reason in regard to pure à priori cognition, and is termed critical philosophy; or it is, secondly, the system of pure reason—a…
Immanuel Kant, The Critique of Pure Reason
states what it is; author linked in the graph
Read the chapter · Open in the reader

Rationality

Overview

In the original texts

Philosophers who discussed Rationality

Related ideas

Place in the tradition