20. Certain cities have crafts that others lack.
This is because it is clear that the activities of the inhabitants of a city necessitate each other, since mutual co-operation is innate in civilization. The necessary activities are restricted to certain inhabitants of the city. They are in charge of them and become experts in the craft(s) belonging to them. These activities become their particular job. They make their living through them and derive their sustenance from them, because (these activities of theirs) are matters of general concern in the city and generally needed. On the other hand, activities not required in a city are not regarded, since there is no profit in them for those who occupy themselves with them.
The activities required for the necessities of life, such as those of tailors, smiths, carpenters, and similar occupations, exist in every city. But activities required for luxury customs and conditions exist only in cities of a highly developed culture, that have taken to luxury customs and sedentary culture. Among such activities are those of glassblowers, goldsmiths, perfumers, cooks, coppersmiths, biscuit bakers, harisah bakers,174 weavers of brocade, and the like. (These activities) exist in different degrees. In accordance with increase in the customs of sedentary culture and the requirements of luxury conditions, there originate crafts (especially) for this kind (of luxury requirements). (The crafts of this) kind will, thus, exist in a particular city, but not in others.
(Public) baths fall into this category. They exist only in densely settled cities of a highly developed civilization as a kind of indulgence resulting from luxury and wealth. Therefore, public baths do not exist in medium-sized towns. It is true that some rulers and chiefs desire (to have baths in their medium-sized cities). They construct them and put them into operation. However, since there is no demand for them from the mass of the people, they are soon neglected and fall into ruins. Those in charge of them speedily leave them, because they have little profit and income from them.
"God holds (His hands) tight together but also opens (them) wide." 175