Beloved in Christ Jesus, the wise men of this world divide all created things into two classes; one class they name substances, the other accidents. The substances are those things that exist through themselves without requiring anything else on which to rest, as the earth, water, air, the heavens, animals, stones, plants, and similar things. The accidents can not exist by themselves, but only by resting on something else, as color, odor, taste, and other such things. But because our knowledge is entirely through the senses, and we are able to know anything only when its accidents fall upon our senses, we have, therefore, knowledge of the accidents rather than of the substances. The eyes are for colors, the ears for sounds, the nose for scents, the tongue for flavors, the touch for heat and cold, for hard and soft. Each sense has its own sphere of knowledge and brings what it has perceived before the imagination, and this hands it over to the reason within, which reads and illuminates the productions of the imagination, judges them, and in this way comes to a knowledge of the substances. But the reason has little light if it is separated from the body, for God has joined soul and body together; and so by means of the senses knowledge becomes definite and complete. For if the soul out of the body were richer in knowledge, it would be in vain that it should be in the body. God and nature have done nothing in vain, and therefore the soul's union with the body ministers to its perfection.