operation of law

Definition from Nolo’s Plain-English Law Dictionary

A way in which someone acquires certain rights or responsibilities automatically under the law, without taking individual action or being the subject of a court order. For example, when one joint tenant dies, any surviving joint tenants obtain title to the jointly owned property; when someone dies without a will, the person's legal heirs automatically become entitled to inherit property from the estate.

Definition provided by Nolo’s Plain-English Law Dictionary.