Practical reason

In philosophy, practical reason is the use of reason to decide how to act. This contrasts with theoretical reason (often called speculative reason), which is the use of reason to decide what to follow. For example: agents use practical reason to decide whether to build a telescope, but theoretical reason to decide which of two theories of light and optics is the best. Practical reason is understood by most philosophers as determining a plan of action. Thomistic ethics defines the first principle of practical reason as "good is to be done and pursued, and evil is to be avoided." For Kant, practical reason has a law-abiding quality because the categorical imperative is understood to be binding one to one's duty rather than subjective preferences. Utilitarians tend to see reason as an instrument for the satisfactions of wants and needs.