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 believe. 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 the "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.

In classical philosophical terms, it is very important to distinguish three domains of human activity: theoretical reason, which investigates the truth of contingent events as well as necessary truths; practical reason which determines whether a prospective course of action is worth pursuing; and productive or technical reason which attempts to find the best means for a given end. Aristotle viewed philosophical activity as the highest activity of the human being and gave pride of place to metaphysics or wisdom. Since Descartes, practical judgment and reasoning have been treated with less respect because of the demand for greater certainty and an infallible method to justify beliefs.

In cognitive research, practical reason is the process of ignoring unproductive possibilities in favor of productive possibilities. It is considered a form of cognitive bias, because it is illogical. An example would be calling all hospitals to look for your missing child, but not checking morgues, as finding his corpse would be 'counter-productive.'