Practical reason

"In theory, there is no difference between theory and practice. But, in practice, there is." -- Jan L. A. van de Snepscheut

In philosophy, practical reason is the application of reason to deciding what to do (reason involved in decision-making or action), as opposed to, for example, deciding whether Isaac Newton's physics is superior to the continental vortex physics; that would be theoretical reason (sometimes called speculative reason).