Practical reason

Practical reason, in philosophy, is the use of reason to decide how to act. It contrasts with theoretical reason, often called speculative reason, 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.

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.'

Practical reasoning is basically goal-directed reasoning from an agent's goal, and from some action selected as a means to carry out the goal, to the agent's reasoned decision to carry out the action. The agent can be a person or a technical device, such as a robot or a software device for multi-agent communications. It is a type of reasoning used all the time in everyday life and all kinds of technology where autonomous reasoning is required. Argumentation theorists have identified two kinds of practical reasoning: instrumental practical reasoning that does not explicitly take values into account, and value-based practical reasoning. The following argumentation scheme for instrumental practical reasoning is given in Walton, Reed & Macagno (2008). The pronoun I represents an autonomous agent.

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