ならいざ知らず【ならいざしらず】

ならいざ知らず is a formal expression used to set aside one case as a possible exception while emphasizing that the main case under discussion is different – usually implying that it would be unreasonable, impossible, or inappropriate. It translates roughly to "maybe for X, but…" or "I don't know about X, but (for Y, it's certainly not the case)."

The literal meaning is "if it were [X], I wouldn't know (whether it's possible), but…" – in other words, the speaker concedes that X might be an exception but firmly states that Y is not.

Structure

The pattern attaches to nouns (with なら) or verb/adjective clauses:

• Noun + ならいざ知らず
• Verb (plain form) + ならいざ知らず
• Adj-i + ならいざ知らず
• Adj-na + ならいざ知らず

Usage notes

• The clause after ならいざ知らず typically contains a negative judgment, criticism, or statement of impossibility regarding the main topic.
• The "exception" mentioned before ならいざ知らず is often something extreme, unusual, or clearly different from the main case – setting up a strong contrast.
• This expression is used in written language and formal speech. In casual conversation, speakers might use ならまだしも or ならともかく instead.
• A common variation is はいざ知らず, which replaces なら with は.