A bastard was a child born to two people who were not married, or whose marriage was later found to be void. He (or she) was not of inferior status under the law but since he was filius nullius (the son of no one), he could not be heir to his parents even if acknowledged as their child: he could not therefore inherit real property. In the earlier Middle Ages an advantage of this rule was that the illegitimate child of a villein did not inherit villein status; he was accounted free. There was a rebuttable presumption at Common Law that children born to a wife were fathered by the husband and were therefore legitimate.
Decisions as to legitimacy often depended on the validity or otherwise of marriages. Matrimony being a sacrament this was a question for the Church to decide. Questions as to the inheritance of land fell to be decided by the secular courts, so two systems of law governed illegitimacy, the law of the Church (Canon Law) and the law of the country, which in England was the Common Law. These two systems sometimes clashed. The Common Law for example, stated that children born out of wedlock could not be legitimated by the subsequent marriage of their parents; Canon Law taught the opposite. Where a marriage was entered into in good faith but later found to be invalid and declared void Canon Law said that the children born before the nullity decree were legitimate. The Common Law held that a void marriage was void for all time and all issue from it were bastards. To avoid conflict the courts of Common Law would ask only whether X was born in or out of wedlock (a question of fact), not whether X was legitimate or not. The latter question would have to go to the Church courts and the Bishop’s answer would be conclusive even though it would be contrary to Common Law principles. –MCO’R