いざ知しらず

expression

I don't know about ... but; it may be possible for ... but

Used to contrast a known or certain situation with an uncertain or exceptional one. Often follows a noun or clause marked by は, meaning 'as for ..., I don't know, but ...'. The second clause typically states something that is true or likely in a different case.

• 彼かれはいざ知しらず、私わたしはそんなことはできない。

  I don't know about him, but I can't do such a thing.

• 昔むかしはいざ知しらず、今いまは誰だれでもスマホを持もっている。

  I don't know about the old days, but nowadays everyone has a smartphone.