2. 用于 be able to do sth(能或會做做某事)。如：
He is able to speak English. 他會說英語。
Everyone here is able to type. 這兒的每一個人都會打字。
He will be able to get about in a week or two. 再過一兩個星期左右他就能走動了。
He studied hard and was able to pass his examinations. 他學習很努力，所以考試及了格。
注：be able to 不僅有多種時態形式(通常不用于進行時或與 be going to 連用)，而且還可以與某些情態動詞連用(通常不與 can 連用)，甚至還可以有非謂語形式。如：
Since his accident he hasn’t been able to leave the house. 自出事之后，他一直未能離開家。
You might be able to persuade him. 你也許能夠說服他。
I hope to be able to do the work. 我希望能干得了這項工作。
I regret not being able to help her. 我很遺憾未能幫助她。
3. able 的比較級和最高級通常是 abler 和 ablest，也可以是 more able 和 most able，有時還可用 better able和best able。如：
You are better able to do it than I (am). 你比我更有能力做這件事。
She’s the person best able to cope. 她是個最能妥善處理問題的人。
4. 若要加強語氣，其前除可very, quite, perfectly等修飾外，有時還可用well修飾。如：
He is quite [well] able to take care of himself. 他完全有能力照顧自己。
He’s a very able student; he’s just too lazy. 他是個很有能力的學生，只是太懶了。
若受just, only just修飾，則表示“只能”“僅能”。如：
I was just able to make out a dark figure in the distance. 我只能看見遠處有個黑影。
5. able的反義詞是unable(不能的，不會的)，不是disable，后者是動詞，其意為“使殘廢”“使無能力”。比較：
They were unable to reach a decision. 他們沒法做出決定。
Now that he was disabled, his house had become a prison to him. 因為他殘廢了，他的房子就成了他的牢籠。