expression, i-adjective
cannot avoid doing; have no choice but to do
Formal/literary expression meaning 'cannot help but do' or 'must do'. Attaches to the imperfective form (未然形) of verbs. Equivalent to ～ないわけにはいかない or ～なければならない, but more bookish.
この状況では、彼も協力せざるを得ないだろう。
In this situation, he will have no choice but to cooperate.
事実を認
I could not help but admit the facts.
Classical negative auxiliary; せざる is its combination with する (未然形 せ + ざる).
Common modern equivalent meaning 'must do', but less formal and more conversational than せざるを得ない.
Similar meaning 'cannot avoid doing', often used when external circumstances force an action. Slightly less stiff than せざるを得ない.
From classical Japanese: せ (未然形 of す, classical equivalent of する) + ざる (negative auxiliary ず in 連体形) + を + 得ない (negative of 得る 'can'). Literally 'cannot get not doing', i.e., 'cannot avoid doing'.