Note that able and capable are both used to say that someone can do something. When you say that someone is able to do something, you mean that they can do it either because of their knowledge or skill, or because it is possible. He wondered if he would be able to climb over the rail... They were able to use their profits for new investments. Note that if you use a past tense, you are saying that someone has actually done something. We were able to reduce costs. When you say that someone is capable of doing something, you mean either that they have the knowledge and skill to do it, or that they are likely to do it. The workers are perfectly capable of running the organization themselves... She was quite capable of falling asleep. You can say that someone is capable of a particular feeling or action. He's capable of loyalty... Bowman could not believe him capable of murder. You can also use 'capable of' when talking about what something such as a car or machine can do. The car was capable of 110 miles per hour. If you describe someone as able or capable, you mean that they do things well. He's certainly a capable gardener.
注意，able和capable都用来表示某人能做某事。able 既可表示因拥有某种知识或技能而能做某事，也可表示客观可能：He wondered if he would be able to climb over the rail (他不知自己能否攀过栏杆)，They were able to use their profits for new investments (他们得以将利润用于再投资)。要注意的是，如果用过去时，则表示实际做了该事：We were able to reduce costs (我们做到了降低成本)。capable既可表示具有做某事的技能或知识，也可表示做某事有较大的可能性:The workers are perfectly capable of running the organization themselves (工人完全能够自己管理这个机构)，She was quite capable of falling asleep (她很容易睡着)。capable 还可表示具有某种情感或能够做出某一行为：He's capable of loyalty (他能做到忠心耿耿)，Bowman could not believe him capable of murder (鲍曼无法相信他会杀人)。capable亦用于指汽车、机器等的性能：The car was capable of 110 miles per hour (这辆车时速可达110英里)。able或capable形容人时表示“有能力的”、“能力强的”：He's certainly a capable gardener (他绝对是一名能干的园丁)。