This is part of a a collection of summaries on the fourteenth century.

The commercial laws of mediæval Europe, like the sumptuary laws, are in direct opposition to several key principles, listed below, that our society has incorporated so thoroughly that we have come to feel them natural and inevitable.

• Self-improvement: The idea of a poor person working his or her way up society's ladder to wealth and fame is a key mythic symbol of some western societies, notably the United States of America. Commercial laws assumed that the only purpose of economic activity was short-term consumption: capital accumulation is alien to them.
• Progress: The typical westerner of today has at least an open mind that any new innovation may be an improvement. Fourteenth century lacked both the historical perspective and the rate of change (relative to random fluctuation) necessary to recognise progress. In any case, it's not trivial to make a watertight case that the fourteenth century represented much progress above anything.

The overriding principle inspiring the commercial laws was that nobody should gain an unfair advantage over anyone else, so that everyone could make a living. There's probably a lot of people out there who'd have some sympathy with that aim, but the practicalities were stifling.

• Innovative tools or techniques were banned. In principle this should stop technological progress dead in its tracks. In reality, however, the high mediæval period was very innovative indeed. So this rule must have been routinely ignored.
• No excess profits, i.e. profits greater than would be needed to provide a reasonable living to the craftsman. What was reasonable was the subject of endless debate, particularly in the field of moneylending. It was possible to be a Christian and a moneylender, but if you charged too high an interest rate you were guilty of the sin of usury. Figures for reasonable rates include 10%, 12.5%, 15% and 20%. The large banking houses charged whatever the market was paying. On a less elevated level the Jews charged higher rates, partly because something like half their revenue disappeared into anti-semitic royal taxes. But the Jews didn't have the financial grunt of the great Italian banking houses.
• No underselling on a set floor price. One might think that this requirement, combined with the one above, constitutes a bar against reducing expenses. Presumably donating the excess to charity would excuse anything.
• Taking on extra apprentices, or employing your wife and children.
• Working when not a member of the guild. One of the few that a modern unionist, or member of a professional society such as the AMA, would recognise.
• Working by artificial light, because it was used to extend working hours. This is another we might see today, as a measure to prevent suffering of workers. But it's not clear that was the principle behind the mediæval laws. A more important factor may have been to permit a larger number of craftsmen without flooding the market.
• Advertising. This could be defined quite widely, for instance, telling someone that your wares were better those of the craftsman down the street.

Other material can be found on my home page, including some on alternate history. I welcome feedback at David.Bofinger@dsto.defenceSpamProofing.gov.au (delete the spamproofing).