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都用來表示某人能做某事。able 既可表示因擁有某種知識或技能而能做某事，也可表示客觀可能：He wondered if he would be able to climb over the rail (他不知自己能否攀過欄杆)，They were able to use their profits for new investments (他們得以將利潤用於再投資)。要注意的是，如果用過去時，則表示實際做了該事：We were able to reduce costs (我們做到了降低成本)。capable既可表示具有做某事的技能或知識，也可表示做某事有較大的可能性:The workers are perfectly capable of running the organization themselves (工人完全能夠自己管理這個機構)，She was quite capable of falling asleep (她很容易睡着)。capable 還可表示具有某種情感或能夠做出某一行爲：He's capable of loyalty (他能做到忠心耿耿)，Bowman could not believe him capable of murder (鮑曼無法相信他會殺人)。capable亦用於指汽車、機器等的性能：The car was capable of 110 miles per hour (這輛車時速可達110英裏)。able或capable形容人時表示“有能力的”、“能力強的”：He's certainly a capable gardener (他絕對是一名能幹的園丁)。