An act sous seingprive, in Louisiana and by the French law, is an act or contract evidenced by writing under the private signature of the parties to it. The term is used in opposition to the authentic act, which is an agreement entered into in the presence of a notary or other public officer. 2. The form of the instrument does not give it its character so much as the fact that it appears or does not appear to have been executed before the officer. 3. The effect of a sous seing prive is not the same as that of the authentic act. The former cannot be given in evidence until proved, and, unless accompanied by possession, it does not, in general, affect third persons; ; the latter, or authentic acts, are full evidence against the parties and those who claim under them.