Reason

Reason is the capacity for rational thought, inference, and justification. In everyday language it refers to the faculty by which humans draw conclusions from information, weigh evidence, and deliberate about what to believe or do. The term derives from Latin ratio, meaning reckoning or calculation.

Philosophy has long treated reason as a source of knowledge and a standard for rational justification. Rationalism emphasizes the role of reason in acquiring knowledge, often with a priority on a priori principles, whereas empiricism emphasizes sensory experience; many thinkers endorse a synthesis (Kant).

Reasoning practices include deductive reasoning, where conclusions necessarily follow from premises; inductive reasoning, where generalizations are supported by observed instances; and abductive reasoning, inference to the best explanation. Formal logic provides frameworks for valid argument structures, while statistics and Bayesian methods address uncertainty.

In cognitive science, reasoning is studied as a cognitive process subject to biases and limits. People often rely on heuristics and display systematic deviations from normative models of rationality. Normative theories prescribe how rational agents ought to reason given evidence.

In science, reasoning underpins hypothesis formation, theory evaluation, and methodological steps. In philosophy, debates center on the nature of a priori knowledge, the scope of reason, and the limits of justification. Historical strands include Aristotelian logic, medieval scholastic disputation, Enlightenment critiques of reason, and Kantian autonomy of rational faculties.

Artificial intelligence advances formal reasoning in machines, using logic programming, automated theorem proving, and probabilistic inference.