Point II. On Law Founded on Common Danger

I. Notion. A law is said to be founded on common danger if it is passed to prevent a general danger. Moreover, it can be founded on the general or common danger either of sin or of fraud. On the danger of sin: as a law which prohibits the reading of evil books; on the danger of fraud: as a law which invalidates clandestine marriages. Laws of this sort are less correctly said by many to be founded on the presumption of the common danger of sin or fraud, because the common danger is not presumed, but certain.

II. Obligation of a law founded on common danger. Laws founded on common danger, or, as the Code has it, passed to prevent a general danger, urge even if in the particular case the danger is absent (can. 21). The reason is that that on which the law is founded, namely common danger, exists. Moreover the legislator very prudently obliges all, even those for whom the danger does not subsist: both because it is expedient that all be obligated uniformly, for example, to avoid scandals necessarily going to arise from the fact that some do not observe the law; and because many would persuade themselves that the danger is absent from them.

Corollary. A law which invalidates clandestine marriages or formless testaments, or prohibits the reading of evil books, urges even if in the particular case the danger of sin or fraud is absent.