Adam Smith noted that the tendency to trade is peculiar to humans. Dogs do not exchange bones for cookies. He called this peculiar tendency, the propensity to truck, barter and exchange:
"The propensity to truck, barter and exchange one thing for another is common to all men, and to be found in no other race of animals."
Wealth of Nations
The father of modern economics, Alfred Marshall, noted that for men to be able truck, barter and exchange effectively, the spiritual life of men should not be ignored:
"The economist does not ignore the mental and spiritual side of life. On the contrary, even for the narrower uses of economic studies, it is important to know whether the desires which prevail are such as will help to build up a strong and righteous character. And in the broader uses of those studies, when they are being applied to practical problems, the economist, like every one else, must concern himself with the ultimate aims of man, and take account of differences in real value between gratifications that are equally powerful incentives to action and have therefore equal economic measures."
Principles of Economics
He understood that it becomes impossible even to exchange goods if men themselves are not good and trustworthy:
"Methods of trade imply habits of trustfulness on the one side and a power of resisting temptation to dishonesty on the other."
Also, the Nobel prize winning economist, Kenneth Arrow, has stressed the importance of virtue for the working of any economy and in particular the modern market economy:
"More basic yet, I will say, is the idea that the price system, in order to work at all, must involve the concept of property (even in the socialistic state there is public property). Property systems are in general not completely self-enforcing. They depend for their definition upon a constellation of legal procedures, both civil and criminal. The course of the law itself cannot be regarded as subject to the price system. The judges and the police may indeed be paid, but the system itself would disappear if on each occasion they were to sell their services and decisions. Thus the definition of property rights based on the price system depends precisely on the lack of universality of private property and of the price system. This ties in with the third hypothesis put forward in section I. The price system is not, and perhaps in some basic sense cannot be, universal. To the extent that it is incomplete, it must be supplemented by an implicit or explicit social contract. Thus one might loosely say that the categorical imperative and the price system are essential complements.”
Gifts and Exchanges