Constitutional provisions do not change, but their operation extends to new matters as the modes of business and the habits of life of the people vary with each succeeding generation. The law of the common carrier is the same to-day as when transportation on land was by coach and wagon, and on water by canal boat and sailing vessel, yet in its actual operation it touches and regulates transportation by modes then unknown, the railroad train and the steamship. Just so is it with the grant to the national government of power over interstate commerce. The Constitution has not changed. The power is the same. But it operates to-day upon modes of interstate commerce unknown to the fathers, and it will operate with equal force upon any new modes of such commerce which the future may develop.[181] Under the commerce clause Congress may enact such legislation as shall declare void and prohibit the performance of any contract between individuals or corporations where the natural and direct effect of such a contract will be, when carried out, to directly, and not as a mere incident to other and innocent purposes regulate to any substantial extent interstate commerce. And “interstate” also includes “foreign commerce.”[182] All the decisions illustrate the principle that Congress in the exercise of its paramount power may prevent the common instrumentalities of interstate and intrastate commercial intercourse from being used in their intrastate operations to the injury of interstate commerce. This is not to say that Congress possesses the authority to regulate the internal commerce of a State, as such, but that it does possess the power to foster and protect interstate commerce, and to take all measures necessary or appropriate to that end, although intrastate transactions of interstate carriers may thereby be controlled.[183] CHAPTER VI THE LAW OF CONTRACTS AND PROPERTY 70. The supreme law of the land provides that no State shall pass any law impairing the obligation of contracts.[184] A contract is an agreement between competent persons to do or not to do a certain thing; the law is part of the contract.[185] An unlawful contract cannot be made, for the so-called contract, being unlawful, has never existed as a contract. The limitation as to contracts in the Constitution is on the States. Thus a State can no more impair its own contracts, by legislation, than it can impair the obligation of the contracts of individuals.[186] A sovereign State is supposed to have a more scrupulous regard to justice, and a higher morality than belongs to the ordinary transactions of individuals.