什么是名词性从句？
名词性从句是指起名词作用的从句。例如（阴影部分为名词性从句）：
·I like what I see.
(和所有分句一样，名词性分句有一个主语 subject和一个动词verb。在本例中，该分句的主语是 "I" 动词是"see."）
·I know that patience has its limits.
(在这个例子中，分句的主语是 "patience"，动词是 "has."）。
将上面的两个例子与下面的例子进行比较：
·I like innovation.
·I know people.
粗体字都是名词nouns。这证明前两个例子中阴影部分的分句从语法功能上来看就是名词。
很多名词性从句都以 "that"、"how "或 "wh"开头（即 "what"、"who"、"which"、"when"、"where "或 "why"）。例如：
·I know that it happened.
·I know how it happened.
·I know why it happened.
如何检查从句是否用作名词
检查短语或分句是否用作名词的一个好方法是尝试将其替换为代词（replacing it with a pronoun）。如果你能做到，那么你的短语或分句就具有名词的功能。
·What I say is true.
(代词测试Pronoun test："It is true." 这证明"What I say" 从语法功能上来看是名词。)
·Show me how they work.
(代词测试Pronoun test："Show me them." 这证明"how they work" 从语法功能上来看是名词。)
名词性从句的简单示例
下面是一些名词性从句的简单示例。在每个例子中，名词性从句用阴影表示，从句的主语用粗体表示，名词性从句的动词用下划线表示。
·I know that the story is true.
·I saw how the accident happened.
·I understand why it was necessary.
·I know who said that.
(通常，开头词（即 "how"、"that "或 "wh"）是名词性从句的主语）。
名词性从句的功能（Function ）
与任何名词一样，名词性从句可以是主语 subject、宾语 object或补语complement。下面是一些名词性从句作为主语、宾语和补语的简单例子。
·Whoever smelt it dealt it.
(这里，名词性从句是主语subject）。
·My command is whatever you wish.
(这里，名词性从句是主语补语subject complement）。
·I will give what you said some thought.
(此处，名词性从句是间接宾语indirect object。）
名词性从句举例
在一个句子中sentence，名词性从句是一个从属性从句dependent clause。换句话说，名词性从句不能独立成为一个完整的思想。
·Ask your child what he wants for dinner only if he's buying.
(该名词性从句是"ask."的直接宾语 direct object。)
·I never know how much of what I say is true.
(该名词性从句是介词的宾语 object of a preposition。)
·Man is what he eats.
(这个名词性从句是主语补语 subject complement。)
在名词性从句的开头选择正确的 "who "和 "whom"。
"Who"是动词的主语。而"Whom"不是。"whoever "和 "whomever "也是一样。
·My relationships are between me and whomever I'm with.
(这里，"whomever "是介词 "with "的宾语 object）。
·My relationships are between me and whoever is interested.
(这里，"whoever "是动词 "is "的主语subject。注意，分句 "whoever is interested"是介词 "between,"的宾语object，但这并不意味着"whoever" 变成了"whomever"。如果你的 "whoever "是动词的主语subject，那么 "whoever "而不是 "whomever "才是正确的）。