Ten: This Art is most useful
"This Art was invented for many useful purposes; it teaches us to understand and love GOD, to follow the virtues and hate the vices, and to confound the erroneous opinions of unbelievers with cogent Reasons; it teaches how to put and solve questions, and how to acquire other sciences in a short time and to reduce them to necessary conclusions according to the requirements of each issue, and it shows how to investigate and find the conditions and properties of things, and above all it elevates the intellect to transcendent points, and many other useful things follow for those who know this Art. (Doctor Illum. in Comp. Art. Dem. in prol.) It teaches how to make good use of memory, intellect and will, and good ways to believe, contemplate, find, direct, preach, expound, solve, judge, counsel, demonstrate and heal, as is said in the Book entitled "The Demonstrative Art", in the third Distinction, on Intention, page 43. (Doctor Illum. in Introd. cap. 1. n. 4.) And you should note, my Son, that under the literal aspect of the said properties I call the sixteen modes of the Demonstrative Art, lies a great secret of my Elemental Figure, namely the way of operating that underlies the way of demonstration.
"Therefore, my Son, in all your reasonong, you should consider whether you can find this Art, and you will always find it if you inquire diligently after it; and if you learn to practice this Art, you will find it admirably useful to reduce whatever reasons you may come across to the cameras of this Art; as you do this you will gain practice in seeing many things in a few, as you match every camera with the angles, and as you combine the cameras with the angles, and the angles with one another and with the terms of the question at hand, and as you derive countless things from them etc.; just as countless general kinds of compounds issue from only four elements according to different ways of combining them." (Doctor Illum. in Introd. cap. 34. n. 2. fol. 29.)