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it is a truism that + clause
该句型中 that 从句是真正的主语，it 为形式主语，常用于引出公认的道理。
It is a truism that people fear the unknown.
人们害怕未知，这是老生常谈。
自明之理；老生常谈
先理解核心含义，再看它在真实句子里的用法。
自明之理；老生常谈
an obvious truth
It is a truism that people fear the unknown.
人们害怕未知，这是老生常谈。
不言而喻的真理
A self-evident or obvious truth.
自明之理
an obvious truth
陈词滥调
A banality or cliché.
It is a truism that regular exercise improves your health.
经常锻炼有益健康，这是不言而喻的道理。
Many teachers repeat the truism that practice makes perfect.
许多老师反复说起那句老生常谈：熟能生巧。
The article begins with a familiar truism about time being money.
文章开头是一句熟悉的老话：时间就是金钱。
该句型中 that 从句是真正的主语，it 为形式主语，常用于引出公认的道理。
It is a truism that people fear the unknown.
人们害怕未知，这是老生常谈。
that 从句作 truism 的同位语，说明该常谈的具体内容。
We accept the truism that money does not buy happiness.
我们接受“金钱买不到幸福”这一老生常谈。
truism 作可数名词，与 about 连用表示“关于某事的常谈”，常含贬义或轻视语气。
She stated a truism about the importance of hard work.
她说了一句关于勤奋工作重要性的老生常谈。
Not this
It is truism that health is more important than wealth.
Use this
It is a truism that health is more important than wealth.
truism 是可数名词，这里指一个具体的道理，前面需要不定冠词 a；汉语没有冠词，所以容易漏掉。
Not this
Your argument seems truism to me.
Use this
Your argument seems true to me.
truism 是名词，不能放在 seem 后作表语形容词；表达“似乎是真实的”要用形容词 true。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
……是自明之理
It is a truism that nothing lasts forever.
没有什么永恒不变是自明之理。
老生常谈；老话
The old truism that honesty is the best policy still applies.
诚实为上策这句老话依然适用。
人所共知的常理
It's a familiar truism that laughter is the best medicine.
笑是最好的药，这是人所共知的常理。
不过是老生常谈
His essay was dismissed as a mere truism.
他的文章被斥为不过是老生常谈。
重复老生常谈
She repeated the truism that practice makes perfect.
她重复了熟能生巧这句老生常谈。
Use truism naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
把 true（真实）+ ism 连起来记：真实主义，即不言自明的道理，说多了就成了老生常谈。
语域：neutral 常见场景：学术写作、正式演讲 truism 指显而易见的事实或老生常谈，通常多用于正式或书面语境，如学术写作、演讲或评论中；日常口语中相对少用。
prism、criticism、racism、sexism 都以 -ism 结尾，读 /ɪzəm/，与 truism 的末尾 /ɪzəm/ 相同；但重音不在最后，所以与 truism 不构成整词押韵。cruise 和 bruise 拼写中有 ruis，与 truism 的 ruis 相同，但读成 /ruːz/（单音节），而 truism 的 rui 是 /ruːɪ/，注意区分。
Dictionary facts from ECDICT, OCTANOVE, WIKTIONARY.