The Constitution of the United States declares that no state shall pass any "law impairing the obligation of contracts."
These propositions may be considered consequent axioms in our jurisprudence: The laws which exist at the time and place of the making of a contract, and where it is to be performed, enter into and form a part of it. This embraces alike those which affect its validity, construction, discharge, and enforcement.
Nothing is more material to the obligation of a contract than the means of its enforcement. The ideas of validity
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and remedy are inseparable, and both are parts of the obligation which is guaranteed by the Constitution against impairment.
The obligation of a contract "is the law which binds the parties to perform their agreement."
Any impairment of the obligation of a contract -- the degree of impairment is immaterial -- is within the prohibition of the Constitution.
The states may change the remedy, provided no substantial right secured by the contract is impaired. Whenever such a result is produced by the act in question, to that extent it is void. The states are no more permitted to impair the efficacy of a contract in this way than to attack its vitality in any other manner. Against all assaults coming from that quarter, whatever guise they may assume, the contract is shielded by the Constitution. It must be left with the same force and effect, including the substantial means of enforcement, which existed when it was made. The guarantee of the Constitution gives it protection to that extent.