Lex posterior derogat legi priori (Latin: "the later law repeals the earlier law") is the principle that, where two legal norms of equal rank conflict, the more recent norm prevails.
Rationale
Legislators are presumed to know the existing law. If they enact a later rule inconsistent with an earlier one, they are taken to have intended to change the law, even if the earlier rule was not expressly repealed. This is known as implied repeal.
Express and Implied Repeal
Modern legislation usually contains a clause expressly repealing or amending earlier provisions. Indonesian laws typically conclude with a provision declaring that earlier rules are revoked or remain in force only so far as they do not conflict with the new law. Implied repeal fills the gaps where drafting is incomplete.
Limits
The principle does not allow a later, lower-ranked regulation to override an earlier statute: the hierarchy of norms (lex superior) is decisive. It also yields where an earlier specific rule meets a later general rule; in that case, courts often hold that the general rule does not impliedly repeal the specific one (lex posterior generalis non derogat legi priori speciali).
In English Law
English courts apply the doctrine of implied repeal, subject to the recognition of "constitutional statutes", such as the Human Rights Act 1998, which may be repealed only expressly, as discussed in Thoburn v Sunderland City Council (2002).