BOOK I

Decorative floral ornament.

...understood that individual arts are composed of two things: the work itself, and the theory behind it. Of these two, the performance of the work is the specific province of those who are trained in individual tasks, while theory is common to all learned people, such as with medicine, music, the rhythm of the veins, and the movement of the feet. However, if a wound must be treated or a patient rescued from danger, a musician will not attend to it; that task belongs properly to the physician. Likewise, in the case of a musical instrument, a physician does not perform, but a musician plays, so that the ears may receive their pleasure from the songs.

Similarly, there is a common discourse between astronomers and musicians regarding the sympathy of the stars and the harmonies of the squares and triangles, the diatessaron a musical interval of a perfect fourth and the diapente a musical interval of a perfect fifth. With geometricians, there is a common discussion regarding vision, which is called in Greek logos optikos theory of optics. With all other disciplines, many things, or indeed all things, are common at least for the sake of debate.

However, the actual undertaking of works, which are brought to elegance by manual labor and handling, belongs to those who are specifically trained in one art to perform it. Therefore, he seems to have done enough who possesses a moderate knowledge of the parts and theories of individual disciplines, particularly those necessary for architecture, so that if there is a need to judge and approve anything regarding these matters and arts, he is not found wanting. But those to whom nature has granted such skill, sharpness, and memory that they are able to possess a deep knowledge of geometry, astronomy, music, and other disciplines, go beyond the duties of architects and become mathematicians. Thus, they are easily able to argue against those disciplines, as they are armed with many weapons of learning. These people, however, are found rarely, so that sometimes...