Pure practical reason is the opposite to impure (or sensibly-determined) practical reason and appears in Immanuel Kant

Immanuel Kant

Immanuel Kant was a German philosopher from Königsberg , researching, lecturing and writing on philosophy and anthropology at the end of the 18th Century Enlightenment....

's Groundwork of the Metaphysics of Morals.

It is the reason that drives actions without any sensible incentives. Human reasoning chooses such actions simply because those actions are good in themselves; this is the nature of good will

Good faith

In philosophy, the concept of Good faith—Latin bona fides “good faith”, bona fide “in good faith”—denotes sincere, honest intention or belief, regardless of the outcome of an action; the opposed concepts are bad faith, mala fides and perfidy...

, which Kant argues is the only concept that is good without any justification, it is good in itself and is a derivative of a transcendental law which affects the way humans practically reason(see practical philosophy

Practical philosophy

The division of philosophy into a practical and a theoretical discipline has its origin in Aristotle's moral philosophy and natural philosophy categories. In Sweden and Finland courses in theoretical and practical philosophy are taught separately, and are separate degrees...

).