Passing to legislation on private matters, we find that any fundamental change in the legal relations of citizens to one another must be effected by the people. The law of the Twelve Tables is itself a _lex centuriata_, and we need only think of laws, such as those on usury, or the _lex Voconia_ on inheritance, as types of a multitude of others. In the matter of civil procedure also a fundamental change, such as that permitting the use of the _formula_ in place of the _legis actio_ in cases falling under the _jus civile_, required legislation.[1185] Yet we feel that it is only a question of degree whether such changes are effected by the people or by the authority of individuals. In matters of substantive law immense changes were brought about by the interpreting authority of the praetor;[1186] while in procedure also much was left to the discretion of pontiffs, magistrates, and jurists. The same principle of division of authority applies to police regulations. Wide as were the coercive powers of the magistrates, sweeping infringements on individual liberty, such as those created by the sumptuary laws, were the work of the people. We may pause here to examine the form of a _lex_, and especially that portion of it which secured its validity—its sanction. A complete law contained three parts: (1) its preamble (_praescriptio_), which described the formal circumstances of its enactment;[1187] (2) the text, in which a minute and exhaustive formalism was rigorously preserved; (3) the sanction, which contained the pains and penalties pronounced against those who violated the provisions of the enactment. A _poena_, however, was not of itself sufficient to constitute a perfect law. A _lex perfecta_ was one which declared an act invalid and imposed a penalty for disobedience. The imposition of a penalty without the declaration of invalidity constituted a _lex minus quam perfecta_.[1188] A law without a sanction was _imperfecta_.[1189] The method of repeal most frequently practised at Rome was rather that of supersession than of the declaration of the nullity of the former enactment. Hence the sanction of laws often gives impunity to those who by obedience incur the pains and penalties pronounced by some previous measure.[1190] Repeal might be either complete or partial, and a series of technical terms was evolved to express this difference.[1191] The attempt of certain laws to secure finality by prohibiting repeal was necessarily futile, as opposed to the whole theory of parliamentary sovereignty.[1192] It is possible, however, that the _leges sacratae_ of the early Republic, such as that which made the tribune sacrosanct, were regarded as unalterable. The _execratio_, which was their sanction, may have been regarded as a fundamental religious obligation, and have been held, as such, to be one of those sacred rights which, as we have seen,[1193] no law professed to infringe.