The most influential thinker and writer of this time was Saint Thomas Aquinas, who in his "Summa Theologica" attempted to harmonize Christianity with the philosophy of Aristotle. His writings and teachings were broad and covered all aspects of economics, politics, church, private property, common goods, trade, interest, usury, ethics and morals, business practices, and social responsibility. More specifically, some of the things he believed and taught were that private property is the best, not because of any natural law, but because it has proven best; commerce and trade are morally lawful only if pursued for a lawful end, such as seeking a modest gain for a livelihood; charging interest on loans is morally wrong because payment is exacted for use that is inseparable from the thing used -- money; a person is entitled to an income only because he labors or because he risks something; the needy have a "natural right" to superfluous income; citizens should participate in their government; the state exists for the individual; woman should be dominated by man; slavery is acceptable; cheating is not permissible; excess profit or loss must be compensated; defective merchandise cannot be sold; and usury is not permitted.35 Saint Thomas'views were still endorsed as late as 1879 by Pope Leo XIII.
In the later part of this same period trade started to flourish again, with Venice being one of the more prominent areas. This was the period when the concepts of partnership, joint ventures, joint ownership, agency, and commission agents were used and refined to fairly standard practices. It was also the early days of development and building of some of the large shipping and trade organizations that would follow.