the ancestor had in his lifetime or at his death, and when the proprietary right is  joined with seisin the heir immediately has a free tenement.1
Who ought to be called a lawful heir.
 We must see who ought to be called a legitimate heir, because [as said below, and  there more fully]2 of children, some are sons and heirs, as those conceived and begotten  of lawful marriages,3 [and some are sons but not heirs]. A legitimate heir is  a son whom the marriage proves to be legitimate,4 as he who 5was born in lawful  wedlock, or one recognized as legitimate in face of the church though in truth there  has been no marriage, [as] when both the husband and the wife were joined in good  faith, believing themselves joined in a lawful union,6 though in truth they are related  by blood or affinity, or in some other way, so that no marriage could exist, 7or if  only one of them so believes, for if a woman weds a married man, believing him in  good faith to be single though he is married to another, and has children by him,  they are adjudged legitimate and heirs,8 whether conceived and born after marriage,  or conceived before marriage and born in wedlock, or conceived during marriage  and born after it has ended, whether it was dissolved by death or, for some reason,  by divorce during their lives, [This is true if9 the espousals or marriage are publicly  contracted between the parents.] provided that if a divorce is pronounced during  their lives and their 10union was clandestine from the outset or contracted, even unwittingly,  within a forbidden degree contrary to church law, the issue of such a union  must be taken as altogether illegitimate, to be aided in no way by the parents' ignorance,  for in so contracting a clandestine marriage they are taken to be not lacking  in knowledge but rather affecting ignorance. Similarly, the issue must be regarded as  illegitimate if both parents, knowing a lawful impediment to exist, presume,  despite every prohibition, to wed in face of the church,11 though this would not  be so if they marry in face of the church in ignorance of the impediment, both,  that is, or only one. But in all cases of clandestine union ignorance will be no  excuse; nor is it such, even if the marriage is publicly contracted, if it is presumptively  contrary to ecclesiastical prohibition. This is established by a decretal  in these words: If between J. and B., man and woman, sentence of divorce has  been canonically pronounced, their children should not suffer injury on that  account if their parents are known to have been married publicly and without any  ecclesiastical objection. Therefore we ordain that their children, born before the  divorce or conceived