A Defect (or Lack) of Form Case is an administrative process that is used when Catholics marry outside the Church. This is technically called a declaration of nullity based on a defect of form. The couple did not exchange vows before a priest and two witnesses in a Catholic church as is required by Canon 1108 §1 of the Code of Canon Law. When Catholics fail to observe this law, the marriage is invalid. These “defect of form” cases account for more than half of all the annulments granted in the Catholic Church.
A defect of form case can only come into play if one of the parties to the marriage is a Catholic (who has not left the Church by a formal act). In a case involving a defect of canonical form due to a wedding taking place “outside” the Catholic Church, the Tribunal must be able to establish certain facts including the following: that the Catholic party was bound by canonical form; that the Catholic party had not left the Church by a formal act prior to or at the time of the wedding; and that the marriage was never subsequently convalidated or otherwise rendered valid in the eyes of the Catholic Church.
Thus, for example, in a case where a Catholic would simply contract marriage by a Justice of the Peace, the marriage would be considered invalid due to lack of proper canonical form.