The validity of a voidable marriage can only be made by one of the parties to the marriage; thus, a voidable marriage cannot be annulled after the death of one of the parties.
A marriage can be voidable for a variety of reasons, depending on jurisdiction. In countries where marriage law is influenced by religion (especially Roman Catholicism) there can be numerous reasons for a marriage to be voidable (see section below).
A diriment impediment prevents a marriage from being validly contracted at all and renders the union a putative marriage, while a prohibitory impediment renders a marriage valid but not licit. An invalid marriage may be subsequently convalidated, either by simple convalidation (renewal of consent that replaces invalid consent) or by sanatio in radice ("healing in the root", the retroactive dispensation from a diriment impediment).
Accordingly, apart from the question of diriment impediments dealt with below, there is a fourfold classification of contractual defects: defect of form, defect of contract, defect of willingness, defect of capacity.
In the canon law of the Catholic Church, an annulment is properly called a "Declaration of Nullity", because according to Catholic doctrine, the marriage of baptized persons is a sacrament and, once consummated and thereby confirmed, cannot be dissolved as long as the parties to it are alive.
A "Declaration of Nullity" is not dissolution of a marriage, but merely the legal finding that a valid marriage was never contracted.
A voidable marriage is a marriage which can be canceled at the option of one of the parties.
It is a valid marriage, but is subject to cancellation if contested in court by one of the parties to the marriage.