ならいざしらず / はいざしらず

The expression ならいざしらず / はいざしらず is used to set aside one case as a possible exception and then emphasize that a different, usually more relevant case does not apply or is unreasonable. It translates roughly to "I don't know about X, but…" or "X might be one thing, but…"

The literal meaning of いざしらず is "I don't know about that" – the speaker acknowledges that something might be acceptable or true for the first case (X), but strongly implies that it is not the case for the second situation being discussed.

Basic usage

The pattern takes a noun, noun phrase, or conditional clause before いざしらず, followed by a second clause that presents the speaker's main point – often a negative judgment, surprise, or strong opinion.

ならいざしらず vs. はいざしらず

Both forms are largely interchangeable. なら carries a slightly stronger conditional nuance ("if it were X"), while は simply topicalizes the exception ("as for X"). In practice, the difference is minimal.

Common patterns

The first clause (X) typically represents an extreme, exceptional, or contrasting case – something far removed from the reality being discussed. Common contrasts include:

• Past vs. present (むかし昔ならいざしらず)
• Expert vs. novice (ぷろプロならいざしらず)
• Child vs. adult (こども子供ならいざしらず)
• Small scale vs. large scale (ひとつ一つやふたつ二つならいざしらず)

This is a formal, written-style expression frequently seen in essays, speeches, and literary contexts. It is rarely used in casual daily conversation.