able，capable和competent都可以表示“有能力的”，均可作定语或表语，但有区别
1. able指人有足够的智慧或力量，聪明能干，也可表示人的体力或身体状况，常用于好事，作表语时后接to do sth.。
the ablest student in the class
班上最有才华的学生
He is an able architect. 他是个很有才干的建筑师。
We aim to help the less able in society to lead an independent life.
我们的宗旨是帮助社会上能力较弱的人独立生活。
The older child should be able to prepare a simple meal.
那个年纪稍大的孩子应当会做一顿简单的饭菜。
The patient was poorly able to sit up. 病人仅能勉强坐起来。
You'll be able to read in peace.
你就能安心地读书了。
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(成功)做了该事：
We were able to reduce costs .我们做到了降低成本。
They were able to achieve a settlement without using military force.
他们没有诉诸武力就解决了问题。
She was able to command the respect of the class.
她赢得了全班的尊敬。
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.= He's certainly an able gardener.
他绝对是一名能干的园丁。
2. capable表示做某事所必需的能力，侧重于有潜能或可能性，可指好事与坏事，语气比able弱，作表语时后接of（doing）sth.。
指具有接受、适应等能力的，强调足以胜任某事；作表语时常后接介词 of，表示“能…的”，其主语可以是人或物。
She is a very capable driver.她是个技术熟练的驾驶员。
He is most capable of leadership. 他极有领导才能。
My mother is a strong, capable woman.
我妈妈是个健壮、能干的女人。
She has become a capable pilot.
她已成为一名有本领的飞行员。
He'll leave the team in your capable hands.
他将把球队交给你这位能手。
He is capable of doing everything.
他什么事都能干。
The hall is capable of holding about three hundred people.
这个大厅能容纳大约三百人。
She is perfectly capable of taking care of herself. 她完全能够照顾自己。
He's quite capable of neglecting his duty. 他很有可能玩忽职守。
That scoundrel is capable of anything. 那个恶棍什么坏事都干得出来。
3.competent着重具有胜任某项工作的技能或所需条件。“足以胜任的；有能力的；称职的，有决定权的”：
Make sure the firm is competent to carry out the work.
要确保这家公司有能力完成这项工作。
He is not competent to the task of teaching English.
他不能胜任英语教学工作。
He is a highly competent teacher.
他是一个十分称职的教师。
He's very competent in his work.
他非常胜任自己的工作。
I had always considered myself a strong, competent woman.
一直以来，我始终认为自己是个女强人。
The people who will be on the committee are moral, cultured, competent people.
进入委员会的人要品行端正，有文化，有能力。
A competent typist is not necessarily a competent secretary.
合格的打字员不一定就是合格的秘书。
I was deemed to be a competent shorthand typist.
我被视为是一名能干的速记打字员。
The case was referred to a competent authority.
事情已交给有关当局处理。
He was a loyal, distinguished and very competent civil servant.
他是一位敬业、优秀而且非常称职的公务员。
Most adults do not feel competent to deal with a medical emergency involving a child.
大部分成年人不懂得如何对儿童实施急救。
The most competent adults are those who know how to do this.
最有能力的成年人是那些知道怎么做的人。
