Meditations 5.14

Reason and the reasoning art [philosophy] are powers which are sufficient for themselves and for their own works. They move then from a first principle which is their own, and they make their way to the end which is proposed to them; and this is the reason why such acts are named Catorthoseis or right acts, which word signifies that they proceed by the right road.

Marcus Aurelius, Meditations 5.14, translated by George Long

Reason and the art of reasoning are in themselves and in their own proper acts self-sufficing faculties. Starting from a principle peculiar to them, they journey on to the end set before them. Wherefore such actions are termed right acts, as signifying that they follow the right way.

Marcus Aurelius, Meditations 5.14, translated by C. R. Haines