Definition
A letter of attorney is a written instrument by which one person (the constituent, or principal) formally authorizes another person (the attorney, or attorney-in-fact) to perform specified lawful acts on the principal's behalf and in the principal's place. The person so appointed acts not in a personal capacity but as a substitute for the principal, and the principal is bound by acts performed within the scope of the authority granted.
The term is now largely synonymous with power of attorney in modern American and English legal usage. Historically, however, "letter of attorney" was the more precise formal designation for the document itself, while "power of attorney" referred to the authority conferred by that document — a distinction that has collapsed in contemporary practice.
Common Language
Modern common usage (Wiktionary): A power of attorney document.
Historical common usage (Webster's 1913): Not separately defined; subsumed under "attorney," meaning one appointed to act for another.
The common usage accurately identifies the document but flattens a distinction legal sources preserve. In legal contexts, the letter of attorney is the instrument; the power of attorney is the legal authority that instrument creates. Researchers working in historical sources should not treat these as perfectly interchangeable terms without checking the surrounding context.
Common Confusion
Letter of attorney is frequently used as an exact synonym for power of attorney in both modern statutes and everyday legal drafting, but older sources — especially English and early American authorities — use the terms with more precision. Burrill's dictionary records the older Latin forms (litera attornati, litteræ procuratoriæ), signaling that the "letter" formulation descends from a documentary tradition in which the physical instrument had its own distinct legal identity. Researchers who encounter "letter of attorney" in pre-twentieth-century materials should not assume all modern power-of-attorney doctrine applies without examining what that document actually authorized.
A separate risk: do not confuse letter of attorney with letters testamentary or letters of administration, which are court-issued instruments authorizing personal representatives to act on behalf of decedents' estates. The superficial similarity in naming has caused index and digest misfiling in historical collections.
Recognized Forms
/SUBTYPES
Historical sources and modern doctrine recognize several functionally distinct variants, now typically analyzed under the power-of-attorney framework:
General letter of attorney: Authorizes broad action across the principal's affairs. Courts have historically construed general grants narrowly where specific authority was expected.
Special (or limited) letter of attorney: Authorizes a specific act or class of acts — executing a deed, collecting a debt, appearing in litigation. Authority expires on completion of the specified act.
Durable letter of attorney: Survives the principal's subsequent incapacity. This form has no firm historical analog; durability is a modern statutory creation requiring explicit language under most current frameworks.
Irrevocable letter of attorney: Coupled with an interest — where the attorney-in-fact holds a stake in the subject matter of the authority — and therefore cannot be revoked unilaterally by the principal. This form carries significant transactional implications and is treated differently at law.
Why It Matters in Research
The primary navigational challenge is terminological drift. In corpus materials spanning several centuries, "letter of attorney" and "power of attorney" appear interchangeably in some sources and as distinct concepts in others. A researcher who searches only one term will miss material indexed under the other.
Older English and colonial American practice used "letter of attorney" as the standard form. The shift toward "power of attorney" as the dominant term accelerated through the nineteenth century and was largely complete by the early twentieth. Sources from Bouvier's era (mid-1800s) often use both terms in the same entry, cross-referencing between them — a sign that contemporaneous readers needed the guidance too.
The corpus contains instruments labeled "letter of attorney" that function as litigation proxies — authorizing an attorney to appear and confess judgment on the principal's behalf. These are structurally related to but functionally distinct from transactional powers of attorney. Confessions of judgment authorized by letter of attorney appear in commercial and debt-collection contexts and have their own procedural history.
Jurisdictional variation in the durability rules, witnessing requirements, and recording obligations means that a letter of attorney valid in one state may be defective in another. Modern research on these questions should begin with the Uniform Power of Attorney Act (2006) and its state adoptions, but historical instruments predate that framework entirely.
Finally, the irrevocable form — the letter of attorney coupled with an interest — surfaces repeatedly in mortgage and conveyancing practice. Spotting this form requires attention to whether the instrument recites consideration flowing to the attorney-in-fact, not just the principal.
Historical Dictionary Support
Black's, Bouvier's, and Burrill's agree on the core definition: a written instrument constituting one person the authorized agent of another for the performance of lawful acts. All three sources treat the principal-and-agent relationship as the organizing framework, and all three note that the appointed person is called the "attorney" in the technical sense — meaning one who acts in another's place — rather than a lawyer.
Bouvier adds the parol-or-sealed distinction, which mattered in an era when sealed instruments carried different legal consequences (consideration, limitation periods, enforceability). That distinction has largely dissolved under modern law but remains relevant to the authentication and interpretation of historical documents.
Burrill is the most etymologically careful, recording the Latin designations litera attornati and litteræ procuratoriæ and signaling that the term "letters of attorney" (plural) was an older common form — consistent with the convention of treating formal legal instruments as "letters" in the medieval and early modern tradition (letters patent, letters testamentary, letters rogatory).
What the historical dictionaries do not address: the durability doctrine, electronic execution questions, and the extensive modern statutory overlay that now governs these instruments in most jurisdictions. For post-1960 developments, the historical dictionaries are structural background only.
Jurisdictional Note
The Uniform Power of Attorney Act (2006), adopted in a majority of states with significant variations, has standardized many rules governing these instruments but has not eliminated interstate conflict on durability, agent liability, and third-party acceptance obligations. Researchers analyzing instruments executed before a jurisdiction's adoption of the UPOAA should apply the law in effect at execution, not current statutory defaults.
Encyclopedia Cross-Reference
Durable Powers of Attorney — Uniform Power of Attorney Act and State Variations (The Law Mind Trusts, Estates & Probate Encyclopedia)