reporting verb + that + clause
在口语中，that 常可省略。
She said that she was tired.
她说她累了。
（用于引导名词性从句，无实义）
（表示结果，常与so或such连用）；引导动词宾语从句,尤其是报道动词或表达信念、知识、感知的动词；引导动词主语从句,尤其是“是”动词或表达判断、意见的动词；引导形容词或被动分词的补语从句；引导修饰副词的从句
Introducing a clause that functions as a noun clause, such as the subject or object of a verb, a complement of an adjective or verb, or in apposition to a noun.
引导宾语从句时，口语中常省略that。
引导动词宾语从句,尤其是报道动词或表达信念、知识、感知的动词
Introducing a clause that is the object of a verb, especially a reporting verb or verb expressing belief, knowledge, perception, etc.
引导动词主语从句,尤其是“是”动词或表达判断、意见的动词
Introducing a clause that is the subject of a verb, especially the 'be' verb or a verb expressing judgement, opinion, etc.
引导形容词或被动分词的补语从句
Introducing a clause that complements an adjective or passive participle.
引导修饰副词的从句
Introducing a subordinate clause modifying an adverb.
引导描述前述报道名词信息内容的从句
Introducing a clause that describes the information content of a preceding reporting noun.
引导结果、后果或影响的从句,尤其与先行词如so或such连用
Introducing — especially, but not exclusively, with an antecedent like so or such — a subordinate clause expressing a result, consequence, or effect.
She told me that the meeting starts at nine.
她告诉我会议九点开始。
用法提示：这里的that引导宾语从句，连接主句和从句，无实义。
It is clear that we need more time.
很明显我们需要更多时间。
用法提示：这里的that引导主语从句，作形式主语it的真正主语。
The box was so heavy that I couldn't lift it.
这个箱子太重了，我抬不动。
用法提示：这里的that与so连用，引导结果状语从句。
在口语中，that 常可省略。
She said that she was tired.
她说她累了。
这里的 that 从句说明形容词或分词所表示感受的内容。
I am glad that you came.
我很高兴你来了。
这种主语从句较正式，日常常改用 it 作形式主语。
That she won the prize is surprising.
她赢得奖项这件事令人惊讶。
so...that 表示“如此……以至于”，引导结果状语从句。
It was so cold that we stayed indoors.
天气太冷了，我们待在屋里。
grammar · medium
易错句子He was late was a problem.
正确表达That he was late was a problem.
英语中从句作主语时必须用从属连词 that 引导，汉语则靠语序直接说出'他迟到是个问题'，学习者容易漏掉 that；加上 that 后，'That he was late' 是合法的主语从句，整个句子结构才成立。
grammar · medium
易错句子The reason he was late is because he missed the bus.
正确表达The reason he was late is that he missed the bus.
reason 本身已包含'原因'之意，表语从句中应使用 that 来直接说明具体原因，不能再接 because，否则语义重复且不符合标准书面语。
grammar · medium
易错句子I want to know that he will come.
正确表达I want to know whether he will come.
want to know 表达的是'去了解一件未知的事'，后面的从句是间接疑问句，须用 whether 或 if 引导；that 从句用于陈述已知信息，用在这里会改变原意。
that 引导陈述性的名词性从句，表示一个事实，在从句中无实义；whether 引导间接疑问句，表示“是否”，与 know、wonder、ask 等动词连用时暗示两种可能性。若从句内容是一个事实，用 that；若内容是“是否”的疑问，用 whether。
that 在名词性从句中只起连接作用，不在从句中作成分，也没有实义；what 在从句中作主语或宾语，意为“什么”或“所……的事物”。当宾语从句结构完整、不缺主语或宾语时用 that；当从句缺少主语或宾语且需要表达“什么”时用 what。
that 常与 so/such 搭配构成 so...that / such...that，表示“如此……以至于”，that 引出结果从句；so 单独作连词表示“因此”，连接结果分句，不与 that 连用。要表达“因为……所以……”时用 so；要表达“如此……以至于”时用 so...that。
以便，为了
She left early so that she could catch the train.
她早早出发以便能赶上火车。
如此…以至于
The damage was such that it could not be repaired.
损坏如此严重，以至于无法修复。
因为，在于
This plan is better in that it costs less.
这个计划更好，因为花费更少。
既然
Now that you're here, let's start the meeting.
既然你来了，我们开始开会吧。
鉴于，考虑到
Given that it's raining, we should stay indoors.
鉴于正在下雨，我们应该待在室内。
that 的主要功能是引导从句。
that 可以引导主语从句。
that 可以引导宾语从句，尤其是动词的宾语。
that 可以引导形容词或被动分词后的补语从句。
that 与 so/such 连用可引导结果状语从句。
以便；所以
She studied hard so that she could pass the exam.
她努力学习以便能通过考试。
既然
Now that everyone is here, let's begin.
既然大家都到了，我们开始吧。
因为；在于
This design is better in that it uses less material.
这个设计更好，因为它使用较少的材料。
我知道我一无所知。
This well-known saying is linked to the Greek philosopher Socrates; it suggests that realizing one's own ignorance is a step toward wisdom.
这句名言与希腊哲学家苏格拉底有关；它表明认识到自己的无知是走向智慧的一步。
我们认为这些真理是不言而喻的：人人生而平等。
This phrase from the U.S. Declaration of Independence (1776) expresses the founders' belief in the equality of all people.
这句短语出自1776年的美国《独立宣言》，表达了开国者们对人人平等的信念。
Dictionary facts from DICTIONARY_API_DEV, ECDICT, WIKTIONARY.
除了…之外；只是
The room is quiet except that the clock ticks loudly.
房间里很安静，只是时钟滴答声很响。