Profits are the difference between the selling price and the cost to the enterpriser, this cost including wages paid to his employees, interest, rent, and upkeep. If there were no variations in the demand for goods, and if the supply of the agents remained constant with no changes in methods of production, managing an enterprise would soon be a very simple matter. Persons of ordinary intelligence would soon learn the conditions of production, and there would be so many persons willing and able to be enterprisers that the enterprisers would receive wages of management but not competitive or monopoly profits. But business conditions are far from being in this static condition. Prices do not remain constant. The amount of labor and capital is constantly varying; new lands are being opened to cultivation; new methods of production are constantly being adopted. In many lines of business the enterpriser who was considered progressive ten years ago would be left hopelessly behind in the race for business if he tried to use the methods of that time today. Out of these competitive and changing conditions arise competitive profits or losses for enterprise. Another source of profits is monopoly. We shall now consider competitive profits and monopoly profits.