よりほかない

よりほかない follows the dictionary form of a verb and means "there is nothing for it but to": you have looked for another way and found none. ほか is "other", so the phrase reads "there is nothing other than doing it". It belongs to writing and serious speech; in conversation the same thing is しかない.

The verb stays in the dictionary form whatever the tense; the past goes on ない, as in ほかなかった. は or に can go after ほか with no change in meaning: よりほかはない, よりほかにない.

• × 歩いたよりほかない → 歩くよりほかなかった

よりほかない, しかない and ざるを得ない

しかない says the same thing in everyday words. ざるをえない得ない takes the ない-form and stresses that you are forced into it against your will; よりほかない only says that every other way is closed. よりしかたがない and よりほかしかたがない are the same pattern with a little more sense of resignation.