Definition
Actio non (from the Latin actionem non habere debet, "ought not to have or maintain his action") is a formal clause appearing in a defendant's special plea in common law pleading. It is the specific language by which the defendant declares that the plaintiff "ought not to have or maintain his aforesaid action" against the defendant. The clause follows immediately after the statement of appearance and defense and precedes the substantive body of the plea, which then sets out the ground or grounds upon which the defendant contends the action cannot proceed.
In a secondary and related sense, Black's Law Dictionary records actio non as a descriptor for a preliminary or preparatory action — one brought to resolve a threshold matter upon which other disputed matters depend. This usage is less common and must be distinguished from the pleading clause.
Common Confusion
Actio non should not be confused with the broader Latin term actio, which refers to a legal action or lawsuit generally. The word non ("not") is integral — actio non is not simply "an action" but the specific denial that any action lies. Researchers unfamiliar with pleading structure sometimes misread actio non as a reference to a class of actions rather than as a clause within a single plea.
Why It Matters in Research
Researchers encountering actio non in historical pleading records must identify which sense is in play. In the overwhelming majority of primary source material — plea rolls, writs, and pleading manuals from the seventeenth through nineteenth centuries — actio non is the formal transitional clause in a special plea, not a reference to a separate type of legal action. Misreading it as a standalone procedural device will produce analytical error.
Because actio non belongs to the architecture of common law special pleading, it is virtually absent from sources post-dating the procedural reforms of the nineteenth century. In England, the Common Law Procedure Act 1852 and subsequent reforms dismantled the formal special plea structure; in American jurisdictions, the Field Code (New York, 1848) and its successors replaced common law pleading with code pleading. Researchers working in post-reform American or English sources will not encounter actio non as a live pleading term. Its appearance in a document is itself a dating signal: the document almost certainly predates or operates outside reformed procedure.
When reading historical treatises — Chitty on Pleading and Stephen on Pleading being the standard reference works cited by Bouvier — note that these works explain actio non as part of a rigid sequential structure. The plea had to follow a precise order: appearance, defense, the actio non clause, then the body of the plea. A plea defective in this sequence was vulnerable to demurrer. Understanding this structure is essential to interpreting plea roll entries correctly.
The secondary meaning recorded in Black's — actio non as a preliminary or preparatory action — appears to be a marginal editorial note rather than a term of widespread usage. Researchers should treat it with caution and should not assume it reflects standard nomenclature in primary sources.
No cross-reference to the matching encyclopedia entries on non-compete, non-disclosure, or non-solicitation agreements is warranted here. Despite the surface similarity of "non," those entries address modern contract law concepts wholly unrelated to this pleading term.
Historical Dictionary Support
Bouvier and Black's agree on the core definition: actio non is the clause in a special plea declaring that the plaintiff ought not to maintain the action. Bouvier is more precise, providing the Latin original (actionem non habere debet) and anchoring the definition directly to Chitty (1 Chit. Plead. 531; 2 id. 421) and Stephen (Plead. 394). These are reliable citations to real treatises; researchers may verify them directly. Black's adds the secondary meaning of a preparatory action without elaborating, and this addition is unsupported by Bouvier. Neither dictionary addresses the post-reform obsolescence of the term, which is the most practically significant fact for modern researchers. Both entries are descriptive of the term's function within the pleading sequence rather than analytical, which reflects the consensus understanding: actio non is a term of art whose meaning is inseparable from the procedural context of common law special pleading.