"To insure that no one gained an advantage over anyone else, commercial law prohibited innovation in tools or techniques, underselling below a fixed price, working late by artificial light, employing extra apprentices and advertising of wares or praising them to the detriment of others. ...

"No economic activity was more irrepressible than the investment and lending at interest of money; it was the basis for the rise of the Western capitalist economy and the building of private fortunes—and it was based on the sin of usury. Nothing so vexed medieval thinking. ... For practical purposes, usury was considered to be not the charging of interest per se, but charging at a higher rate than was decent. This was left to the Jews as the necessary dirty work of society, and if they had not been available they would have had to be invented. ...

"Merchants regularly paid fines for breaking every law that concerned their business, and went on as before."