Definition
Latin: "after the day." A phrase appearing in two distinct historical contexts:
1. In pleading: A characterization of a plea asserting that payment was made after the day it became due. A plea of payment post diem acknowledges that the obligation existed and was owed on the appointed day, but asserts that satisfaction occurred after that date — a substantively different defense than a plea that payment was made on time (solvit ad diem).
2. In old practice: The return of a writ after the day assigned for its return. An accompanying fee was payable in such cases for the late return.
Common Confusion
Post diem is easily conflated with its complement, solvit ad diem ("he paid on the day"), and should be distinguished carefully. Solvit ad diem is a plea that payment was made punctually, on the day performance was due. Post diem, by contrast, concedes lateness. The practical significance is not trivial: a post diem plea may succeed as a defense to the debt itself (the obligation was ultimately discharged) while still leaving the pleading party exposed to liability for damages arising from the delay. Researchers encountering these Latin formulae in pleading records should treat them as legally distinct, not interchangeable.
Why It Matters in Research
Post diem is a term of art tied almost exclusively to the formal pleading systems of common law practice — particularly the era of special pleading before code pleading reforms swept through American jurisdictions in the mid-nineteenth century and English practice under the Judicature Acts of 1873–75. Researchers working in pre-reform pleading records, court rolls, or early American case law will encounter post diem as a shorthand for a recognized and structured plea form with defined legal consequences.
The key research trap: post diem does not mean that the debt was forgiven or that the creditor lost the right to recover. It means only that the payment was late. Older sources, including Burrill and the Comyns Digest (Pleader, 2), treat it as a formal plea category — meaning courts evaluated it under specific pleading rules about what had to be alleged, traversed, or confessed and avoided. A researcher treating post diem loosely as mere acknowledgment of payment will miss its technical force.
The writ-return usage is a separate procedural matter. In old English practice, officers returning writs were expected to do so by an assigned day; post diem return triggered a fee. This usage is essentially obsolete and unlikely to appear outside of historical records or glossaries of court administration.
Neither usage survives in modern pleading practice by name, but the underlying distinction — timely versus untimely performance — is fundamental to contract and debt law and appears in modern doctrine under different vocabulary (anticipatory breach, cure periods, conditions precedent, payment defenses).
Historical Dictionary Support
The four historical sources are in close agreement, with minor variations in emphasis. Black's (both editions) and Burrill lead with the pleading usage and treat the writ-return fee as secondary. Rapalje & Lawrence focus exclusively on the pleading definition and cross-reference solvit post diem — the more developed entry in their dictionary, which explains the doctrinal mechanics in greater detail. Burrill explicitly flags the Latin pleading context before defining the term, which helpfully signals to researchers that this is a technical formula, not a generic phrase.
All four sources cite Cowell for the writ-return and fee usage and point to Comyns Digest (Pleader, 2) for the pleading usage. These citations are consistent across editions and reflect the stable, narrow scope of the term in historical legal literature. No source attempts a broader or more modern application.
What the historical dictionaries do not address: the evidentiary consequences of a successful post diem plea, what damages might nonetheless be recoverable after late payment was established, or how the plea interacted with statutes of limitations on debt actions. Researchers needing that depth should move from these dictionary entries to the treatise literature on common law pleading — Chitty on Pleading being the standard reference for English practice.