This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
The term " contracts " shows that the protection of this clause is limited to those created by agreement. Rights arising by positive law, not contractual in their nature are not protected by this clause, whatever other clause of the Constitution may be invoked to protect them. Thus a statute providing that purchasers of a railway at a foreclosure sale may incorporate, is not a contract, and may be'repealed by the state, notwithstanding this clause.1 So it has been held that a resolution of a municipal council allowing a street railway to build a road and requiring it to pave between the tracks and for three feet on each side, and to keep such paving in repair is not a contract within the protection of this clause.2 So where A began the study of law when certain requirements for admission to the bar were in force and before he applied for admission such requirements were changed, it was held that A had no contractual right to admission under the old requirements; but that to be admitted he must comply with the new requirements.3 A statute providing that a by-law of a beneficial society is not a part of its contract of insurance unless in the certificate of insurance or attached thereto, does not impair the obligation of such contracts as far as concerns by-laws passed after such statute.4 The term " contracts " in this clause means genuine contracts.5 These may be either express6 or implied.7 A contract made in another state is protected by this clause of the Constitution.8 It does not include quasi-contracts.9 A right to recover money paid under duress10 or by mistake11 is a right resting in quasi-contract and not in contract, and may therefore be taken away by subsequent statute. So a penal liability created by statute may be abolished at any time before judgment, even if an action is pending.12 Thus a subsequent statute may take away the right to recover money lost at gambling.13 However, the repeal of a statute declaring a forfeiture of all interest where usurious interest is contracted for or received does not affect the right to recover the excess of usurious interest over the legal rate, in an action for money had and received.1*
5 Hooker v. Burr, 194 U. S. 415.
1 Grand Rapids, etc., Ry. v. Os-born, 193 U. S. 17 (affirming 130 Mich. 248: 89 N. W. 967) : People v. Cook. 148 U. S. 397 (affirming 110 N. Y. 443; 18 N. E. 113).
2 Binninger v. New York, 177 N. Y. 199; 69 N. E. 390.
3 In re Day, 181 111. 73; 50 L. R. A. 519; 54 N. E. 646.
4 Hunziker v. Supreme Lodge, - Ky. - ; 78 S. W. 201.