able ：最常用詞，多用于褒義，著重指多方面的，經常性的，或潛在性的能力。有時也指高超、非凡的能力。
capable ：語氣弱于able，指有能力、有潛力或有條件做某事，常與of連用。
competent ：強調具有能勝任某項工作的足夠技能或其它所需的條件。
英語四級真題
This week's announcement of a new iPhone by a management team led by Tim Cook, who replaced Mr Jobs as chief executive in August, was generally regarded as competent but uninspiring.
出自-2012年12月閱讀原文
Studies show they're also perceived as more competent than women in STEM Science, Technology, Engineering, and Mathematics fields.
2017年12月四級真題（第二套）閱讀 Section C
英語六級真題
As a result, Black people are thought of a less competent and as having colder personalities.
出自-2015年12月閱讀原文
As a result, " Black " people are thought of a less competent and as having colder personalities.
2015年12月六級真題（第一套）閱讀 Section C
柯林斯高階英漢雙解學習詞典釋義
ADJ-GRADED
能勝任的;稱職的
Someone who is competent is efficient and effective.