Practice is to theory what the feet are to the head. [ E. de Girardin ]

Behavior is the theory of manners practically applied. [ Mme. Necker ]

Gray, dear friend, is all theory, and green life's golden tree. [ Johann Wolfgang von Goethe ]

Theory looks well on paper, but does not amount to anything without practice. [ H. W. Shaw ]

Theory, from whatever source, is not perfect until it is reduced to practice. [ Hosea Ballou ]

The knowledge of the theory of logic has no tendency whatever to make men good reasoners. [ T. B. Macaulay ]

The philosophy of reasoning, to be complete, ought to comprise the theory of bad as well as of good reasoning. [ John Stuart Mill ]

He that would be a master must draw from the life as well as copy from originals, and join theory and experience together. [ Jeremy Collier ]

Education must bring the practice as nearly as possible to the theory. As the children now are, so will the sovereigns soon be. [ Horace Mann ]

The value of a principle is the number of things it will explain; and there is no good theory of disease which does not at once suggest a cure. [ Emerson ]

Those who are conversant with books well know how often they mislead us when we have not a living monitor at hand to assist us in comparing practice with theory. [ Junius ]

Not only so, but scarcely any attempt is entirely a failure; scarcely any theory, the result of steady thought, is altogether false; no tempting form of error is without some latent charm derived from truth. [ Whewell ]

No man was ever endowed with a judgment so correct and judicious, in regulating his life, but that circumstances, time and experience would teach him something new, and apprize him that of those things with which he thought himself the best acquainted he knew nothing; and that those ideas which in theory appeared the most advantageous were found, when brought into practice, to be altogether inapplicable. [ Terence ]