incapable

Compared meaning: not enough or not able (adjective).

比较义项：不够、不能胜任或缺乏必要的东西（形容词）。

• inadequate

  Describes a thing, amount or situation that fails to meet a particular need or standard, not a person's ability; typically followed by 'for'.

  描述事物或数量未能满足某种特定需要或标准，而非评价人的能力；常与介词 for 连用。

  The old bridge was inadequate for modern truck traffic.

  这座旧桥已不能满足现代卡车通行的需要。

• incapable 本词

  Focuses on a person's inability to perform an action, often due to circumstance or lack of capacity, without necessarily judging skill; used with 'of' plus a verb-ing form.

  侧重人无法完成某个动作，往往是因为处境或能力所限，并不一定评价其技能；常与 of doing 连用。

  After the injury, he was incapable of lifting even light weights.

  受伤后，他连轻的东西都举不起来。

• incompetent

  Negatively judges a person's skill or professional ability, implying repeated failure to perform a job properly; stronger and more critical in tone than incapable.

  负面评价一个人的技能或职业能力，暗示其屡屡不能把工作做好；语气比 incapable 更强烈，更带批评意味。

  The incompetent electrician left wires exposed and dangerous.

  那个不称职的电工把电线裸露在外，十分危险。

• deficient

  Describes something lacking a specific necessary component, quality or amount within it, typically followed by 'in'; neutral, technical register common in nutrition or systems.

  描述某事物缺少某种必需的成分、品质或数量，常与介词 in 连用；语气中性，常用于营养、系统等技术性语境。

  The soil was deficient in nitrogen, so the plants grew slowly.

  这片土壤缺氮，所以植物长得很慢。

Inadequate, incapable, incompetent and deficient mean not enough or not able. Inadequate describes a thing that fails to meet a need. Incapable means a person cannot do something, without judging skill. Incompetent judges a person's poor job skill. Deficient means lacking a necessary part.

这四个词都可表示不够或不能，但适用对象和语气不同：inadequate 侧重事物或数量不足以满足某种需要；incapable 侧重人（或事物）因能力或处境所限而做不到某事，语气较中性；incompetent 专指人缺乏做好某工作所需的技能，带有批评意味；deficient 侧重缺少某种必需的成分或素质，语气中性、技术性强。这里不比较 inadequate 表示自卑、觉得能力不够好的用法，也不比较 incompetent 在法律或医学语境中表示不具备资格的用法。