(11) Along the same line of principles, it is good to keep in mind the distinction between public interest and private interest.  Regarding the former, society and the public authorities must protect and encourage it; as to the latter, the State must only guarantee freedom.  Whenever a matter is of public interest, public law intervenes, and what , on the contrary, corresponds to private interests must be referred to the private sphere.  Marriage and the family are of public interest; they are the fundamental nucleus of society and the State and should be recognized and protected as such.  Two or more persons may decide to live together, with or without a sexual dimension but this cohabitation is not for that reason of public interest.  The public authorities can not get involved in this private choice.  De facto unions are the result of private behavior and should remain on the private level.  Their public recognition or equivalency to marriage, and the resulting elevation of a private interest to a public interest, damages the family based on marriage.  In marriage a man and a woman constitute a community of the whole of life which is ordered by its very nature to the good of the spouses and the generation and up-bringing of offspring.  In marriage, different from de facto unions, commitments and responsibilities are taken on publicly and formally that are relevant for society and exigibile in the juridical context.