Under common law, a bastard was nullius filius, the son of no man. The grammarian John of Genoa, meanwhile, explained the Latin origin of the word stepfather thus:

In one scenario, the law had vanished the father. In another, the stepfather was a distorting mirror that hid the true father behind a lie. So far in this book I have mostly written about fathers to legitimate, biological offspring, but the parameters of fatherhood went beyond the confines of the nuclear family. Step-parenthood and fathering bastards created problems for a system that was based on primogeniture. What kind of paternal authority could an outsider, who did not bestow patrimony, bring to his stepchildren? How could a man be a father to bastards when they might not even bear his name? Fatherhood that fell outside the ideal model might be perceived to be distorted, misleading or empty: but through these looking glasses we find reflected back essential truths of medieval fatherhood. We see its reliance on affection, authority, the household and lineage – but not all of these at all times, or in equal measure.