Trade involves the transfer of goods or services from one person or entity to another, often in exchange for money. A system or network that allows trade is called a market.
Economists have never allowed their analysis to be influenced by psychologists of their time, but have always framed for themselves such assumptions about psychical processes as they have thought it desirable to make.
Joseph Schumpeter, History of Economic Analysis, 1945. p. 27
Men did not make the earth. ... It is the value of the improvements only, and not the earth itself, that is individual property. ... Every proprietor owes to the community a ground rent for the land which he holds.