Wiktionary
n. (context philosophy English) The use of reason to decide how to act.
Wikipedia
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.
Usage examples of "practical reason".
So far as practical reason is entitled to lead us we shall not look upon actions as obligatory because they are the commands of God, but look upon them as divine commands because we feel an inner obligation to follow them.
As during these labours I have advanced pretty far in years (this very month, into my sixty-fourth year), I must be careful in spending my time, if I am to carry out my plan, of furnishing a metaphysic of nature, and a metaphysic of morals, in confirmation of the truth of my critique both of speculative and of practical reason, and must leave the elucidation of such obscurities as could at first be hardly avoided in such a work, and likewise the defence of the whole, to those excellent men who have made it their own.
That it was fear which drove the old man to disfigure his Critique of rational psychology is shown also by this, that his attacks on the sacred doctrines of the old dogmatism are far weaker, far more timid and superficial, than in the First Edition, and that, for the sake of peace, he mixed them up at once with anticipations which are out of place, nay, cannot as yet be understood, of the immortality of the soul, grounded on practical reason and represented as one of its postulates.
The practical reason is this: You simply cannot be effective in politics unless you join in the process of compromise and conciliation whereby free men merge little groups into big groups until they accomplish a government.
Although she hadn't anticipated it when she'd refused Toomey's initial demand that she go to London on the Friday, a practical reason for her remaining at Europol had emerged.
It required very little effort to see the practical reason motivating these researches.
Since, in the long run, every planetary society will be endangered by impacts from space, every surviving civilization is obliged to become spacefaring--not because of exploratory or romantic zeal, but for the most practical reason imaginable: staying alive.