XVII. (56) "And God caused to rise out of the earth every tree which is pleasant to the sight and good for food, and the tree of life he raised in the middle of the Paradise, and also the tree of the knowledge of good and evil." He here gives a sketch of the trees of virtue which he plants in the soul. And these are the particular virtues, and the energies in accordance with them, and the good and successful actions, and the things which by the philosophers are called fitting; (57) these are the plants of the Paradise. Nevertheless, he describes the characteristics of these same trees, showing that that which is desirable to be beheld is likewise most excellent to be enjoyed. For of the arts some are theoretical and not practical, such as geometry and astronomy. Some, again, are practical and not theoretical, such as the art of the architect, of the smith, and all those which are called mechanical arts. But virtue is both theoretical and practical; for it takes in theory, since the road which leads to it is philosophy in three of its parts--the reasoning, and the moral, and the physical part. It also includes action; for virtue is art conversant about the whole of life; and in life all actions are exhibited. (58) Still, although it takes in both theory and practice, nevertheless it is most excellent in each particular. For the theory of virtue is thoroughly excellent, and its practice and observation is a worthy object to contend for. On which account Moses says that the tree was pleasant to the sight, which is a symbol of theoretical excellence; and likewise good for food, which is a token of useful and practical good.