All these forms of monopoly interfere with free competition and they cover a great many of the things which are in common use by the people.[15] Recent investigations have shown that the number of commodities which are either wholly or in large part controlled by monopolistic combines is larger than people commonly realize. A certain amount of legal monopoly is essential in order to encourage research and invention.[16] Men will not strive to invent new machines and appliances if the invention at once becomes common property. Natural monopolies arise from the essential nature of things and it is difficult to see how most of them can ever be avoided. We cannot very well have two competing street railways on the same street, for example. There would then be little room in the street for anything else. Artificial monopolies are often objectionable because they enable a few persons or corporations to obtain excessive prices from the public; but even an artificial monopoly can in some cases be advantageous. Occasionally some corporation, by producing things on a very large scale, is able to do it so cheaply that small producers are driven out of business. The large concern then finds that it has become a monopoly, but so long as it does not arbitrarily raise prices the public is not injured by the mere fact that a monopoly exists. [Sidenote: The principle of freedom in economic relations] =Freedom of Contract.=—An outstanding characteristic of modern economic organization is the encouragement of private enterprise through freedom of contract. By the laws of the land the worker is not forced to take employment from anybody; he may contract with whomsoever he pleases. He may even join with other workers in a union and make a collective bargain, that is, a group of workers, large or small, may contract with one or more employees or with a group of employers. The employer, on his side, is not forced to hire anybody; he also has freedom of contract. It is true, of course, that this legal theory of individual freedom does not find complete exemplification in actual practice. The right of the wage-earner to bargain collectively is not everywhere conceded by employers; the right of the employer to hire non-union men is not everywhere conceded by the unions (see p. 406). The landlord is not obliged to rent his house, nor the tenant to stay against his will. Both are bound by the terms of their contract and no more. Buying and selling are conducted with similar freedom. All this affords a great spur to private initiative. Everyone depends for his own prosperity and advancement upon the skill with which he can use his freedom. A well-known English writer, Sir Henry Maine, once declared that the progress of civilization has been a movement _from status to contract_. He meant that in primitive times all men had their careers virtually determined for them by the station in which they were born. The child of