say

Compared meaning: express or share information in words (verb).

比较义项：用言语表达、传递信息（说、告诉、解释、交谈）（动词）。

• say 本词

  Focuses on the exact words or message expressed, often followed by a direct quotation or a clause; it does not take a personal object (you cannot "say someone something").

  着重表达出的具体话语或内容，常接直接引语或从句；不能直接接人作宾语（不能说“say someone something”）。

  Did she say what time the meeting starts?

  她说会议几点开始了吗？

• explain

  Focuses on making something clear or understandable, often about reasons, methods or meanings; when a person is added, it needs "to" (explain something to someone).

  着重把某事讲清楚、讲明白，常涉及原因、方法或含义；如果要接人，必须用“to”（explain something to someone）。

  Can you explain how this machine works, please?

  你能解释一下这台机器是怎么运作的吗？

• tell

  Requires a listener as a direct object; used for giving information, instructions or an account to a specific person, as in "tell me what happened".

  后面必须直接接人作宾语，用于把信息、指示或经过告诉某个具体的人，如“tell me what happened”（告诉我）。

  Please tell me what happened at the meeting.

  请告诉我会议上发生了什么事。

• talk

  Emphasizes a two-way conversation or exchange between people, usually with "to/with" and "about"; it is not normally followed directly by a piece of information.

  强调人与人之间的双向交流或对话，通常与“to/with”和“about”搭配；一般不直接接具体信息作宾语。

  We should talk about our plans for the weekend.

  我们应该谈谈周末的计划。

These four words mean giving information in words. Say focuses on the exact words spoken, with no person as object. Tell always needs a listener. Talk stresses a two-way conversation. Explain focuses on making something clear and understandable.

这四个词都表示“用言语表达或传递信息”，但语法结构和侧重点不同：say着重说出的内容本身，tell后面必须直接接听话人，talk强调双方来回的交谈过程，explain则着重把事情讲清楚、讲明白。中国学习者常因中文都译作“说/告诉”而混用这几个词的搭配方式，需要特别注意。

Compared meaning: to suggest something as a hypothesis (verb).

比较义项：假设，假定（动词）。

• say 本词

  Mainly used in imperative or conditional form to set up a quick hypothetical for casual discussion; informal, common in everyday speech rather than writing.

  主要用于祈使句或条件句中，快速提出一个假设场景以供随意讨论；语气非正式，多见于日常口语而非书面语。

  Say you won a million dollars—what's the first thing you'd buy?

  假设你中了一百万美元——你最想买的第一样东西是什么？

• suppose

  More formal, used to introduce a supposition treated as true for the sake of an argument or logical exercise, often followed by 'that'.

  语气更正式，用来引出一个为了论证或逻辑推演而暂且当作真实的假设，常与“that”连用。

  Suppose the train is late; how would that affect our plans?

  假设火车晚点了，那会怎样影响我们的计划？

Say and suppose both introduce a hypothetical for discussion. Say is casual and spoken. Suppose is more formal, common in logical reasoning. Say can also mean 'to speak'; suppose can also mean 'to guess'; those meanings are not compared here.

这两个词都可用来提出一个假设场景以供讨论，意思相近，但语气和用法有别：say 更口语化，suppose 更正式，常用于逻辑推演。这里不比较 say 的“说，讲”义，也不比较 suppose 的“猜想，认为很可能”义。