The term "ab initio" is a Latin phrase meaning "from the beginning." In legal terminology, particularly under the law of torts, Trespass ab initio} refers to a situation where an individual initially enters another’s property lawfully, but later misuses that authority or commits an unlawful act. Due to the misuse, the entry itself is treated as unlawful from the outset—hence, "trespass from the beginning."
This doctrine plays a key role when someone has legal permission to enter (e.g., under statutory authority or license), but by misusing that authority or committing a wrongful act, their lawful entry is retrospectively considered illegal.
Example: If a police officer enters a house lawfully with a warrant but commits theft while inside, the entry is converted into trespass ab initio.
Thus, the accurate and most appropriate interpretation of "trespass ab initio" is "trespass from the beginning."