Reason is the capacity for logical and coherent thought. It is what allows us to draw inferences, solve problems, and make judgments. It is not the same as intelligence, which is the ability to learn and apply knowledge. It is not the same as rationality, which is the quality of being reasonable. Reason is a faculty, a process, and a norm. It is the faculty we use when we think. It is the process of drawing conclusions from premises. It is the norm that tells us what conclusions are justified. Philosophers have debated whether reason is universal or culturally shaped, whether it is purely formal or emotionally inflected, and whether it is the same in all humans.

Kant argued that reason is the source of morality and the foundation of knowledge. Hume argued that reason is the slave of the passions, that it can tell us how to achieve our goals but not what goals to pursue. In the 20th century, critical theorists questioned the Enlightenment's faith in reason, pointing to its use in domination and exploitation. Cognitive scientists have shown that human reasoning is often biased and emotional. But reason remains central to philosophy, science, and law. It is what we appeal to when we ask for evidence, when we test arguments, when we try to persuade. Reason is not infallible. But it is the best tool we have.

Types of reason

• Deductive. Drawing necessary conclusions from premises.
• Inductive. Generalizing from observations.
• Practical. Reasoning about what to do.
• Theoretical. Reasoning about what is true.

Reason is not the same as logic. Logic is the formal study of valid reasoning. Reason is the broader capacity that logic studies.