Rational

Rational is an adjective describing what is governed by reason rather than by emotion, prejudice, or habit. It derives from the Latin rationalis, from ratio meaning reason or calculation. In everyday usage, a rational conclusion or action is one that is coherent, justifiable, and based on evidence.

In mathematics, rational has more precise meanings. Rational numbers are numbers expressible as the quotient of two integers a/b with b nonzero. They form the set Q and include familiar fractions as well as integers. Their decimal expansions either terminate or repeat. Rational functions are ratios of two polynomials, and their domain excludes points where the denominator vanishes; these functions are studied in algebra and analysis for properties such as asymptotes and zeros.

In philosophy and logic, rationality refers to the capacity to reason or to act in ways that are consistent with coherent principles of logic or maximizing expected value. Rationalism is the view that reason is a primary source of knowledge. In social science, rational choice theory models agents as making decisions to maximize expected utility, while bounded rationality notes limits to information, computation, and time.

The term also appears in related phrases such as rationalization, rational thinking, and rational processes, contrasting with irrational or emotional responses. The nuances depend on context, but across fields the core idea is orderly, justified reasoning and systematic behavior.