Incapacity is the noun: the lack of ability to do things, or to do some particular thing. It is more formal than can’t and even stiffer than incapable. You mainly meet it in three rooms.

Incapacity isIncapacity是 the noun名詞：the lack of ability to do things指做事情的能力不足，or to do some particular thing或做某件特定事情。It is more formal than can't它比can't更正式 and even stiffer than incapable甚至比incapable還要生硬。You mainly meet it你主要會遇到它 in three rooms在三個場合。

At work and in insurance, incapacity is being unable to work because of illness or injury — papers talk of incapacity benefit or leave.

At work and in insurance在職場和保險裡，incapacity is being unable to workincapacity指無法工作 because of illness or injury因病或受傷——papers talk of incapacity benefit or leave公文會說incapacity benefit或incapacity leave。

In law, mental or legal incapacity means the person is not allowed to sign contracts or make big decisions; that is a specialist use, not kitchen-table talk.

In law在法律上，mental or legal incapacity meansmental或legal incapacity指 the person is not allowed to sign contracts or make big decisions這個人不被允許簽合約或做重大決定；that is a specialist use這是專業用語，not kitchen-table talk不是日常餐桌上的話題。

And in rather bookish English, incapacity to act just means not being able to.

And in rather bookish English而在比較書面的英文裡，incapacity to actincapacity to act just means就只是指 not being able to沒辦法做到。

Though actually, everyday speech almost never uses this word: people say can’t, isn’t able to, or, for a lasting condition, disability.

Though actually不過其實，everyday speech almost never uses this word日常講話幾乎不用這個字：people say can't, isn't able to大家會說can't、isn't able to，or, for a lasting condition如果是長期的狀況，disability就說disability。

Capacity is the ability (to hold, to do, to take on); incapacity is the hole where that ability should be. It is not a fancy spelling of incapable — one is a noun, one is an adjective.

Capacity is the abilityCapacity是能力 (to hold, to do, to take on)（容納、做到、承擔的能力）；incapacity is the hole where that ability should beincapacity則是那個能力該在卻不在的空洞。It is not a fancy spelling of incapable它不是incapable的花式拼法——one is a noun一個是名詞，one is an adjective一個是形容詞。