e words are, that "no State shall
pass any law impairing the obligation of contracts." The general
operation of all such laws is to impair that obligation; that is, to
discharge the obligation without fulfilling it. This is admitted; and
the only ground taken for the distinction to stand on is, that, when the
law was in existence at the time of the making of the contract, the
parties must be supposed to have reference to it, or, as it is usually
expressed, the law is made a part of the contract. Before considering
what foundation there is for this argument, it may be well to inquire
what is that obligation of contracts of which the Constitution speaks,
and whence is it derived.

The definition given by the court in _Sturges v. Crowninshield_ is
sufficient for our present purpose. "A contract," say the court, "is an
agreement to do some particular thing; the law binds the party to
perform this agreement, and this is the obligation of the contract."

It is indeed probable that the Constitution used the words in a somewhat
more popular sense. We speak, for example, familiarly of a usurious
contract, and yet we say, speaking technically, that a usurious
agreement is no contract.

By the obligation of a contract, we should understand the Constitution
to mean, the duty of performing a legal agreement. If the contract be
lawful, the party is bound to perform it. But bound by what? What is it
that binds him? And this leads us to what we regard as a principal
fallacy in the argument on the other side. That argument supposes, and
insists, that the whole obligation of a contract has its origin in the
municipal law. This position we controvert. We do not say that it is
that obligation which springs from conscience merely; but we deny that
it is only such as springs from the particular law of the place where
the contract is made. It must be a lawful contract, doubtless; that is,
permitted and allowed; because society has a right to prohibit all such
contracts, as well as all such actions, as it deems to be mischievous or
injurious. But if the contract be such as the law of society tolerates,
in other words, if it be lawful, then we say, the duty of performing it
springs from universal law. And this is the concurrent sense of all the
writers of authority.

The duty of performing promises is thus shown to rest on universal law;
and if, departing from this well-established principle, we now follow
the teachers who instruct us that