💬 命题：能判断真假的陈述句💬 Propositions: sentences that can be true or false
上一片里，小算盘用散点图从数据里找线索；这一片它回到事务所的另一张桌子——审句子。不是每句话都能当线索：只有能判断真假的陈述，才叫命题。Last leaf, the little calculator hunted for clues in data with scatter plots. This leaf it returns to another desk in the office — sentence inspection. Not every sentence can serve as a clue: only statements that can be judged true or false are propositions.
第 1 步：能盖章的句子Step 1: Sentences that can be stamped
怎么判断一句话是不是命题？看它能不能盖上「真」或「假」的章。How do we tell whether a sentence is a proposition? Check whether it can take a TRUE or FALSE stamp.
「2 + 2 = 4」盖上真章，「猫会飞」盖上假章——它们都是命题：真假能判断。注意：说错了不影响身份，「猫会飞」是假命题，但仍然是命题。“2 + 2 = 4” takes a TRUE stamp; “cats can fly” takes a FALSE stamp — both are propositions: their truth can be judged. Note: being wrong does not disqualify a sentence — “cats can fly” is a false proposition, and still a proposition.
那「明天下雨」呢？我现在还判断不了呀。What about “it will rain tomorrow”? I cannot judge it yet.
第 2 步：现在不知道，但终会落定Step 2: Not known yet, but bound to settle
暂时不知道，不等于不能判断。「明天下雨」到明天就会落定为真或假——就像抛起的硬币，落下时必是一面。真假迟早能定的陈述，仍然是命题。Not knowing yet is not the same as being unjudgeable. “It will rain tomorrow” will settle into true or false once tomorrow comes — like a coin spinning in the air, it must land on one side. A statement whose truth will settle is still a proposition.
哪些句子会被门卫拦在档案室外？Which sentences get stopped at the archive door?
第 3 步：这些句子进不了档案Step 3: These sentences stay outside
问句（你好吗？）、命令句（快关窗！）、感叹句（哇！）都不判断任何事，没有真假可谈，不是命题。还有「x > 3」这种：x 没定下来，真假说不准，也不算命题。Questions (“How are you?”), commands (“Close the window!”), exclamations (“Wow!”) — none of them claim anything, so there is no truth to judge; not propositions. Same for “x > 3”: until x is fixed, its truth is undecided, so it is not a proposition either.
🎮 你来当门卫（1 分钟）🎮 Your turn: sentence gatekeeper (1 minute)
4 轮句子卡送到你面前，每轮藏着 2 个命题。点出它们，盖好章，收进档案盒。Four rounds of sentence cards are headed your way, two propositions hidden in each. Tap them, stamp them, and file them away.
一句话记住它：命题 = 能判断真假的陈述句；问句、命令、感叹句，还有没定数的 x > 3，都进不了档案。Remember it in one line: a proposition is a statement that can be judged true or false — questions, commands, exclamations and unsettled “x > 3” stay outside the archive.
命题非真即假：说错了也是命题（假命题）A proposition is true or false: even a wrong one is a proposition (a false one)暂时不知道（明天下雨）仍然是命题——真假终会落定Not known yet (“it will rain tomorrow”) is still a proposition — its truth will settle问句、命令句、感叹句没有真假；含未定字母的句子也不算Questions, commands and exclamations have no truth value; sentences with an unsettled letter do not either
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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