What it means
ならいざしらず presents A as an exceptional or relatively understandable case, then contrasts it with B, which is surprising, unacceptable, or difficult to accept. It is most often used in formal or written language and commonly follows a noun. The expression conveys “I do not know about A, but B” rather than making a neutral conditional statement.
Usage note
ならいざしらず is normally followed by a comma and a contrasting second clause; it is not usually used as a complete sentence by itself. The predicate in the second clause can be made polite independently, while ならいざしらず itself remains unchanged.
How to use it
専門家ならいざしらず、初心者にこの説明は難しいです。
I do not know about experts, but this explanation is difficult for beginners.
専門家ならいざしらず、初心者にこの説明は難しい。
I do not know about experts, but this explanation is difficult for beginners.