Translation guide
The English word "illegitimate" has several distinct meanings. This guide organizes them by practical use: describing children born outside marriage, actions or things that are not legal or authorized, and reasoning that is logically invalid. For each meaning, natural Japanese expressions are provided, with notes on formality and common usage.
Describing a child whose parents were not married at the time of birth.
Standard, neutral term for an illegitimate child. Used in legal and formal contexts.
彼は私生児として生まれた。
He was born an illegitimate child.
Legal term meaning 'child born out of wedlock'. Used in official documents and discussions of family law.
非嫡出子の相続権が問題になった。
The inheritance rights of illegitimate children became an issue.
Literally 'child outside marriage'. A more modern, slightly less formal term than 私生児, often used in news reports.
婚外子に対する差別は減少している。
Discrimination against illegitimate children is decreasing.
Means 'hidden child', often implying a child kept secret, typically from an extramarital affair. Carries a nuance of scandal.
Not a direct translation of 'illegitimate'; use only when secrecy is implied.
彼には隠し子がいるという噂だ。
There's a rumor that he has an illegitimate child (kept secret).
Describing an action, government, or authority that is not legally valid or not sanctioned by law.
Adjectival form meaning 'illegal'. The most common and direct translation for actions that break the law.
違法な手段で金を稼いだ。
He earned money through illegitimate means.
Also means 'illegal' or 'unlawful', often used in compound terms like 不法侵入 (trespassing). Slightly more formal than 違法.
不法な政府を打倒する。
Overthrow the illegitimate government.
Means 'lacking legitimacy'. Used for authorities or regimes that are not recognized as rightful.
その政権は正統性のないものと見なされている。
The regime is considered illegitimate.
Describing a conclusion, argument, or reasoning that does not follow logically from the premises.
Means 'logically incorrect'. The most straightforward way to describe an illegitimate argument.
それは論理的に誤った結論だ。
That is an illegitimate conclusion.
Means 'not valid' or 'unsound'. Used in logic and debate to describe an argument that does not hold.
その推論は妥当でない。
The reasoning is illegitimate.
Means 'unjust' or 'unreasonable'. Can be used for illegitimate claims or demands, but is broader than pure logic.
Often implies unfairness rather than strict logical fallacy.
不当な要求を拒否した。
He refused the illegitimate demand.
Both mean 'illegal', but 違法 is more common for general law-breaking, while 不法 is often used in fixed legal terms (不法行為 = tort, 不法滞在 = illegal stay). 違法 is slightly more everyday.
In casual conversation, directly saying 私生児 can sound blunt or old-fashioned. Often, Japanese speakers use circumlocutions like 結婚していない両親の子 (child of unmarried parents) to avoid stigma. Use with care.