sure

Compared meaning: certain, having no doubt (adjective).

比较义项：确信的，有把握的（形容词）。

• sure 本词

  A general everyday word for being certain of a fact, plan or future event; commonly follows 'I'm sure (that)...'; not limited to judging one's own ability, can be about anything or anyone.

  日常用语，表示对某个事实、计划或未来的事情很确定；常用于“I'm sure (that)…”句型；不局限于评价自己的能力，也可以指任何事或任何人。

  I'm sure I locked the front door before we left.

  我确定我们出门前锁了前门。

• confident

  Focuses on self-assurance, especially about one's own ability or future performance; commonly paired with 'confident of/about doing something'; carries a positive, encouraging tone.

  侧重对自己的能力或未来表现有信心；常与“confident of/about doing something”搭配；语气积极、令人振奋。

  She's confident she'll get the promotion this year.

  她对自己今年会获得晋升很有信心。

Sure and confident both mean certain, but sure is neutral and everyday, used for facts, plans, or events. Confident focuses on believing in your own ability or future performance, and sounds more positive. Sure alone as a casual reply, like 'Sure!', is not compared.

sure 和 confident 在这个意义上很接近，都表示“确信、有把握”，但 sure 只是单纯表示对事实或情况的确定，语气中性、日常；confident 则强调对自身能力或表现的信心，语气更积极，常用于谈论能力和前景。这里不比较 sure 用作口语应答“好的，当然”（如“Sure!”）的用法。

Compared meaning: without doubt, of course (adverb).

比较义项：确定无疑地；当然（副词）。

• certainly

  Certainly is the most neutral and formal member, usable as a sentence adverb before the verb or alone as a firm, polite affirmative reply.

  certainly 是三者中最中性、最正式的词，可放在动词前作句子副词，也可单独使用作坚定、礼貌的肯定回答。

  The manager certainly appreciated the effort her team put in.

  经理确实很感激她的团队所付出的努力。

• sure 本词

  Sure is the most informal, used mainly alone as a casual affirmative reply in speech, rarely placed before a verb in this sense.

  sure 是三者中最口语化的词，主要单独使用，作随意的肯定回答，在这个意义上很少放在动词前使用。

  "Can you send me the file?" "Sure, I will do it now."

  “你能把文件发给我吗？”“当然，我现在就做。”

• surely

  Surely often expresses the speaker's confident expectation or hope, sometimes seeking agreement, and can sound persuasive or slightly rhetorical rather than purely factual.

  surely 常用来表达说话人自信的预期或希望，有时是在寻求认同，语气可能带有说服性或修辞性，而不只是陈述事实。

  Surely you don't expect me to finish this by tomorrow?

  你该不会真的指望我明天之前完成这个吧？

Certainly, sure, and surely all mean 'of course'. Certainly is neutral and formal, used before a verb or alone. Surely often shows hope or expectation, mainly in questions. Sure is the most informal, usually a short answer alone. Sure meaning 'confident' is not compared here.

这三个词在这一“确实、当然”的意义上很接近，容易混淆，但语气和搭配不同：certainly最正式中性，可放在动词前也可单独作答；surely常带说话人的期待或修辞语气，多用于反问句；sure最口语化，通常单独用作随意的肯定回答。这里不比较 sure 作形容词表示“确信的”这一用法。