15. The crafts require teachers.

It ⁷⁸ should be known that a craft is the habit ⁷⁹ of something concerned with action and thought. In as much as it is concerned with action, it is something corporeal and perceptible by the senses. Things that are corporeal and perceptible by the senses are transmitted through direct practice more comprehensively and more perfectly (than otherwise), because direct practice is more useful with regard to them.

A habit is a firmly rooted quality acquired by doing a certain action and repeating it time after time, until the form of (that action) is firmly fixed.⁸⁰ A habit corresponds to the original (action after which it was formed). The transmission of things one has observed with one's own eyes is something more comprehensive and complete than the transmission of information and things one has learned about. A habit that is the result of (personal observation) is more perfect and more firmly rooted than a habit that is the result of information. The skill a student acquires in a craft, and the habit he attains, correspond to the quality of instruction and the habit of the teacher.

Furthermore, some crafts are simple, and others are composite. The simple ones concern the necessities. The composite ones belong to the luxuries. The simple crafts are the ones to be taught first, firstly because they are simple, and (then) because they concern the necessities and there is a large demand for having them transmitted. Therefore, they take precedence in instruction. (But) the instruction in them, as a consequence, is something inferior.

The mind, (however,) does not cease transforming all kinds of (crafts), including the composite ones, from potentiality into actuality through the gradual discovery of one thing after the other, until they are perfect. This is not achieved all at one stroke. It is achieved in the course of time and of generations. Things are not transformed from potentiality into actuality all at one stroke, especially not technical matters. Consequently, a certain amount of time is unavoidable. Therefore, the crafts are found to be inferior in small cities, and only the simple (crafts) are found there. When sedentary civilization in (those cities) increases, and luxury conditions there cause the use of the crafts, they are transformed from potentiality into actuality.⁸¹