under necessity

For example, he said a lot of attempts to use necessity had failed because the actions taken under necessity must be the only way to safeguard a state's interests.

It should be done under necessity only.

If you wish to swear so as to escape the stake, one oath will not suffice for me, nor ten, nor a hundred, nor a thousand, because you dispense each other for a certain number of oaths taken under necessity, but I will require a countless number.

He is not under necessity, because there is no constraint which compels him to choose the right end, rather than the wrong one.

Such a being is neither under necessity nor chance.