A Latin term meaning "from the beginning." Used to indicate that some fact existed from the start of a relevant time period.
Ab initio
A homeowner believed that his contract with a roof builder would only become valid if the roof builder started performing. In fact, since the contract was properly formed and authorized, it was valid ab initio.
"[B]ecause the prerogative of the Alabama Supreme Court to say what Alabama law is merits respect in federal forums, a law challenged at first opportunity and invalidated by Alabama's highest court is properly regarded as null and void ab initio, incapable of effecting any change in Alabama law or establishing a voting practice for [purposes of the Voting Rights Act of 1965]."