2. 用于 be able to do sth(能或会做做某事)。如：
He is able to speak English. 他会说英语。
Everyone here is able to type. 这儿的每一个人都会打字。
He will be able to get about in a week or two. 再过一两个星期左右他就能走动了。
He studied hard and was able to pass his examinations. 他学习很努力，所以考试及了格。
注：be able to 不仅有多种时态形式(通常不用于进行时或与 be going to 连用)，而且还可以与某些情态动词连用(通常不与 can 连用)，甚至还可以有非谓语形式。如：
Since his accident he hasn’t been able to leave the house. 自出事之后，他一直未能离开家。
You might be able to persuade him. 你也许能够说服他。
I hope to be able to do the work. 我希望能干得了这项工作。
I regret not being able to help her. 我很遗憾未能帮助她。
3. able 的比较级和最高级通常是 abler 和 ablest，也可以是 more able 和 most able，有时还可用 better able和best able。如：
You are better able to do it than I (am). 你比我更有能力做这件事。
She’s the person best able to cope. 她是个最能妥善处理问题的人。
4. 若要加强语气，其前除可very, quite, perfectly等修饰外，有时还可用well修饰。如：
He is quite [well] able to take care of himself. 他完全有能力照顾自己。
He’s a very able student; he’s just too lazy. 他是个很有能力的学生，只是太懒了。
若受just, only just修饰，则表示“只能”“仅能”。如：
I was just able to make out a dark figure in the distance. 我只能看见远处有个黑影。
5. able的反义词是unable(不能的，不会的)，不是disable，后者是动词，其意为“使残废”“使无能力”。比较：
They were unable to reach a decision. 他们没法做出决定。
Now that he was disabled, his house had become a prison to him. 因为他残废了，他的房子就成了他的牢笼。