impairing the obligation of contract

IMPAIRING THE OBLIGATION OF CONTRACTS. The Constitution of the United 
States, art. 1, s. 9, cl. 1, declares that no state shall "pass any bill of 
attainder, ex post facto law, or law impairing the obligation of contracts." 
     2. Contracts, when considered in relation to their effects, are 
executed, that is, by transfer of the possession of the thing contracted 
for; or they are executory, which gives only a right of action for the 
subject of the contract. Contracts are also express or implied. The 
constitution makes no distinction between one class of contracts and the 
other. 6 Cranch, 135; 7 Cranch, 164. 
     3. The obligation of a contract here spoken of is a legal, not a mere 
moral obligation; it is the law which binds the party to perform his 
undertaking. The obligation does not inhere or subsist in the contract 
itself, proprio vigore, but in the law applicable to the contract. 4 Wheat. 
R. 197; 12 Wheat. R. 318; and. this law is not the universal law of nations, 
but it is the law of the state where the contract is made. 12 Wheat. R. 213. 
Any law which enlarges, abridges, or in any manner changes the intention of 
the parties, resulting from the stipulations in the contract, necessarily 
impairs it. 12 Wheat. 256; Id. 327; 3 Wash. C. C. Rep. 319; 8 Wheat. 84; 4 
Wheat. 197. 
     4. The constitution forbids the states to pass any law impairing the 
obligation of contracts, but there is nothing in that instrument which 
prohibits Congress from passing such a law. Pet. C. C. R. 322. Vide, 
generally, Story on the Const. Sec. 1368 to 1891 Serg. Const. Law, 356; 
Rawle on the Const. h.t.; Dane's Ab. Index, h.t.; 10 Am. Jur. 273-297.