Definition
The act of writing between the lines of a completed or executed instrument; also, the words, phrases, or passages so inserted. Interlineation encompasses both the physical act of adding matter between existing lines and the resulting addition itself.
An interlineation may occur before or after a document's execution, and the legal consequences depend heavily on which: pre-execution interlineations are generally valid if noted at the time of signing or attestation, while post-execution interlineations raise more serious concerns about document integrity and authenticity.
Common Language
Modern common usage (Wiktionary): A notation made between the lines, especially in a handwritten document; interlining.
Historical common usage (Webster's 1913): The act of interlining. That which is interlined; a passage, word, or line inserted between lines already written or printed.
Editorial note: The common and legal meanings are close in form but diverge significantly in consequence. In ordinary usage, writing between lines is a minor textual technique. In law, the same act can void a deed, invalidate an affidavit, or raise a presumption of fraud — making interlineation far more consequential than the descriptive term alone suggests.
Common Confusion
Interlineation is sometimes conflated with erasure or alteration more broadly. The distinction matters: an erasure removes existing text, while an interlineation adds text between existing lines. Legal instruments may treat each differently. Some authorities treat both as species of material alteration, but courts have historically applied separate presumptions to each. A document with an unexplained erasure may raise different evidentiary questions than one with an unexplained interlineation.
Why It Matters in Research
Timing is everything. Historical sources are consistent that the legal effect of an interlineation turns on when it was made — before or after execution — and by whom. Researchers working with historical deeds and conveyances should watch for this distinction: pre-execution interlineations noted in an attestation clause or memorandum were generally treated as harmless; post-execution interlineations made by a party in interest were often grounds to void the instrument entirely, even if the change was immaterial.
The affidavit context is a separate trap. Rapalje & Lawrence notes a distinct rule: interlineations or erasures in the jurat of an affidavit generally preclude the affidavit from being read in court. Researchers examining historical litigation records should be alert to this as a procedural objection that could make an otherwise substantive affidavit disappear from a case record.
Third-party interlineations carry different presumptions than party-made ones. Bouvier distinguishes between interlineations made by a party to the instrument and those made by strangers. Historically, a party's own post-execution interlineation — material or not — was treated more harshly, often voiding the deed, while stranger interlineations triggered different analysis.
Modern instruments have reduced the practical frequency of this issue, but it remains live in probate and estate litigation involving handwritten (holographic) wills, where interlineations appear regularly and courts must determine whether they represent valid amendments or unauthorized alterations.
Cross-corpus connection: Questions of interlineation frequently arise alongside issues of execution formalities, attestation, and the law of alterations to negotiable instruments. In the negotiable instruments context, material alteration doctrine — which has statutory codification in the Uniform Commercial Code — largely supplanted older common-law interlineation rules, so the applicable framework depends on whether the instrument at issue is a negotiable instrument or a deed/will.
Historical Dictionary Support
The five source dictionaries converge on the basic definition: interlineation is writing between lines, and it applies to completed written instruments. There is no meaningful disagreement on the core concept.
The more instructive divergences appear in consequence. Bouvier is the most substantive, drawing the timing distinction explicitly and noting that a party's own post-execution interlineation — whether material or immaterial — historically voided the deed. This reflects a strict common-law rule designed to prevent self-serving alteration. Rapalje & Lawrence adds the affidavit-jurat rule, which Bouvier and Burrill do not address, suggesting this was a distinct procedural rule rather than a general principle of interlineation law.
Burrill's entry frames interlineation as a conveyancing term specifically, which accurately reflects where most historical doctrine developed — in the context of deeds and written instruments to land. Black's (both editions) keeps the definition neutral and instrument-agnostic, consistent with its general reference character.
What the historical dictionaries collectively underemphasize is the law of negotiable instruments, where material alteration — which subsumes interlineation — developed along a parallel but distinct track. Researchers should not assume that historical conveyancing rules on interlineation apply in the commercial paper context.
Jurisdictional Note
The common-law rule treating a party's post-execution interlineation as voiding a deed was not uniformly applied, and some American jurisdictions developed more nuanced tests focused on materiality of the change. Modern courts rarely apply the strict voiding rule categorically. For wills specifically, state probate statutes govern whether interlineations constitute valid amendments, and practice varies substantially.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Alteration of Instruments; Execution of Instruments; Wills — Formal Requirements.