The state and federal governments are prohibited from passing ex post facto laws. These prohibitions found in the state and federal constitutions are construed as referring only to statutes relating to the punishment of crime. (See above, § 59.) Retrospective legislation in general is not expressly prohibited, and unless it impairs vested rights of property or of contract it is not unconstitutional. Thus the legislature may by subsequent statute make valid the recording of a deed which by reason of some informality was not legally recorded; and as to any rights arising after the passing of the legalizing act, the defective record which is legalized will be just as effectual as though the recording had been in the first instance regular and lawful; but as to any person who has acquired an interest in the property for a good consideration which would be impaired by treating the defective recording as lawful, the legalizing statute can have no effect.

In general the legislature may change or modify the rules of procedure without impairing vested rights. For instance, it may extend the period of limitation within which an action may be brought, and the person against whom it is brought cannot complain; or it may shorten the period, and the person entitled to bring the action cannot complain if a reasonable time has been left to him within which to bring an action for the assertion of his rights (Mitchell v. Clark). The general rule is this, that remedies for the protection of property rights or for enforcing the obligation of a contract may be modified, even as to property already existing or contracts already made, with this exception that the legislature cannot by such changes or modifications of statutory provisions take away all substantial remedy for the protection of property or the enforcement of contract obligations and leave the property owner or party to the contract without any substantial remedy (Bron-son v. Kinzie and McCracken v. Hay ward).

The right to enact retrospective statutes for the purpose of legalizing acts already done, which are for some technical defect in the method of procedure invalid, is especially recognized with reference to the organization and conduct of municipal corporations (Mattingly v. District of Columbia). Here no private rights are involved, and the legislature may legalize proceedings which are invalid if they might have been valid had they been duly authorized in the first place.

The retrospective legislation, therefore, which is unconstitutional is that which amounts to an ex post facto law or which impairs some vested property or contract right. Legislation is in its nature prospective and not retrospective, and even a so-called retrospective statute is in effect no more than a prospective statute, applicable to conditions which have arisen and are in existence when the statute becomes applicable.