"The mere practical architect is not able to assign sufficient reasons for the forms he adopts; and the theoretic architect also fails, grasping the shadow instead of the substance. He who is theoretic as well as practical, is therefore doubly armed; able not only to prove the propriety of his design, but equally so to carry it into execution."
The Architecture of Marcus Vitruvius Pollio, trans. Joseph Gwilt (London, 1826), pp 3-4