(Latin: "(the) father is", abbreviated from pater est quem nuptiae demonstrant, "(the) father is (he) to whom the marriage points")
A legal principle of assumption, used in paternity cases. In common terms, the principle may be expressed thusly:
If you are born to a married woman, her husband is by legal definition your father, absent hard evidence to the contrary.
Though DNA evidence of paternity is now available as a more reliable guide, the pater est rule still holds effect for all cases where paternity is unchallenged.