2. Marriage is considered by all civilized nations as the only source of legitimacy; the qualities of husband and wife must be possessed by the parents in order to make the offspring legitimate; and furthermore the marriage must be lawful, for if it is void ab initio, the children who may be the offspring of such marriage are not legitimate. 1 Phil. Ev. Index, h. t.; Civ. Code L. art. 203 to 216.
4. A conclusive, presumption of legitimacy arises from marriage and cohabitation; and proof of the mother's irregularities will not destroy this presumption: pater est quem nuptiae demonstrant. To rebut this presumption, circumstances must be shown which render it impossible that the husband should be the father, as impotency and the like. 3 Bouv. Inst. n. 300-2. Vide Bastard; Bastardy; Paternity; Pregnancy.