Theory of Pleading Doctrine Law and Legal Definition

Theory of pleading doctrine is a principle that one must prove a case exactly as pleaded. According to this doctrine, a complaint must proceed upon some definite theory and a plaintiff must succeed on that theory or not succeed at all. However this theory has been abolished under the federal rules. Pursuant to Fed. R. Civ. P. 8, a legal theory is not necessary if a plaintiff sets forth sufficient factual allegations to state a claim showing that s/he is entitled to relief under some cognizable legal theory.

The Federal Rules of Civil Procedure abolish the "theory of pleadings" doctrine which formerly required a plaintiff to succeed only on those theories pleaded. Rather, the federal rules, and the decisions construing them, evince a belief that when a party has a valid claim, s/he should recover on it regardless of his/her counsel's failure to perceive the true basis of the claim at the pleading stage, provided always that a late shift in the thrust of the case will not prejudice the other party in maintaining his/her defense upon the merits.[Mayan v. Chemetron Invs., Inc., 2000 U.S. Dist. LEXIS 21640 (S.D. Iowa June 19, 2000)]