Definition
Single adultery is a classification of adultery in which only one of the two parties engaged in the sexual act is married to someone else. The unmarried participant is the one who is "single" in the relevant sense — not that the relationship itself is singular in any other way. The married participant commits adultery; the unmarried participant, in jurisdictions recognizing the distinction, is treated as a lesser or differently situated wrongdoer.
The contrasting classification is double adultery, where both participants are married to other persons at the time of the act.
Common Language
Modern common usage (Wiktionary): "Single" ordinarily means unmarried, alone, or constituting one unit. "Adultery" means voluntary sexual intercourse between a married person and someone other than their spouse.
Historical common usage (Webster's 1913): "Single" — consisting of one only; individual; separate. "Adultery" — violation of the marriage bed; voluntary sexual intercourse of a married person with a person other than the offender's husband or wife.
The compound term "single adultery" does not mean adultery committed once, or adultery involving one act. It means adultery in which only one of the two parties carries the status of being married. A researcher relying on ordinary English would likely misread this term entirely.
Common Confusion
Single adultery is frequently confused with simple adultery or adultery generally, partly because the single/double distinction has not been universally adopted and is absent from many modern legal codes. The classification belongs to an older framework — particularly relevant in fault-based divorce law and, historically, in criminal adultery statutes — that parsed moral and legal culpability based on the marital status of each party. In jurisdictions that never adopted the distinction, "adultery" encompasses both single and double scenarios without further subdivision. Researchers should not assume the single/double framework applies in any given jurisdiction without confirming it in period-appropriate sources.
Why It Matters in Research
This term is a research trap in two directions. First, its plain-English meaning is almost certainly wrong if you read it without context. Second, its legal significance depends entirely on which jurisdiction and which era you are researching.
The single/double adultery distinction mattered most in three contexts: (1) criminal adultery statutes, where some jurisdictions imposed different penalties or treated the unmarried party differently from the married one; (2) fault-based divorce proceedings, where a petitioner's ability to obtain a divorce on adultery grounds, or a respondent's ability to raise the other party's adultery as a defense or counterargument, could turn on whether the adultery was single or double; and (3) civil actions for criminal conversation and alienation of affections, now largely abolished, where the characterization of the act could affect standing or damages.
In the Law Mind corpus, this term is most likely to appear in historical family law materials, nineteenth- and early twentieth-century treatises on domestic relations, and older criminal codes. Modern family law encyclopedia entries discussing fault-based divorce grounds will typically treat adultery as a unified concept without the single/double distinction, reflecting its erosion in contemporary practice.
When reading historical pleadings, opinions, or treatises that invoke "single adultery," pay attention to whether the jurisdiction treated the unmarried party as a wrongdoer at all. In some frameworks, the unmarried participant in single adultery bore no legal liability; in others, both parties were culpable but to different degrees.
Historical Dictionary Support
Black's Law Dictionary is the primary source for this term and states it plainly: the distinction between single and double adultery exists "in some jurisdictions," with single adultery committed where only one party is married and double adultery where both are. The qualifier "in some jurisdictions" is doing significant work — Black's is signaling that this is not a universal classification.
Historical legal dictionaries that do engage the term tend to echo Black's framing without expanding on it. What the historical sources largely omit is any practical account of how the distinction was applied procedurally, what consequences followed from it, or which specific jurisdictions recognized it. Researchers should not treat the single/double framework as a settled common-law doctrine; it appears to have been a legislative and judicial refinement adopted selectively rather than a universal principle.
Jurisdictional Note
The single/double adultery distinction was recognized in some American jurisdictions, particularly in the context of criminal adultery statutes and fault-based divorce law, but was never universal. Most modern jurisdictions have abolished criminal adultery statutes entirely, and no-fault divorce has rendered the distinction practically moot in contemporary family law. Researchers working in pre-twentieth-century materials should verify whether the jurisdiction in question formally adopted this classification before relying on it.
Encyclopedia Cross-Reference
Divorce -- Fault-Based Grounds (Adultery, Cruelty, Desertion, Imprisonment) (The Law Mind Family Law Encyclopedia)