1. 谓语主格的定义
1.1 第一种定义
一个名词或者名词短语，可能会出现在某种不及物动词或被动动词之后，或者可能将某种不及物动词或被动动词的含义补充完整，且仍然与这个动词的主语一样，表示同样的人或事物，则称这个名词或名词短语称为谓语主格(the predicate nominative)，又称为谓语性名词(predicate noun)，或谓语性名词短语。
例如，在句子中，“The author of this book is my brother，”“brother”是述语(predicate)，但是它不是动词的宾语，因为动词“is”判定“author”和“brother”是等效的，同于“author”是主格，“brother”也必须是一样是主格。我们可以说，“The author of this book is I”(主格)，不是“is me”(注意格)。
解析模型示例：
(1). Tennyson is a poet.
poet…………………..普通名词，单数，性为男性，主格——位于动词“is”之后的谓语主格。
(2). Washington was elected present in 1789.
present……………………..普通名词，单数，性为男性，主格——位于动词“was elected”之后的谓语主格。
更多例子：
(1). And , Saxon , I am Roderick Dhu .
(2). The earth is a planet.
(3). Mary still seemed a queen ( = was a queen in seeming, or appearance ).
(4). King William of Prussia became Emperor of Germany in 1871 .
(5). He was a man , take him for all in all, I shall not look upon his like again.
1.2 第二种定义
谓语主格(predicate nominative)，又称为谓语名词(predicate noun)，是名词或代词的传统语法术语，或者跟在连系助动词之后的名义上的主语，通常使用动词“to be”连接，谓语主格的当代术语称为主语补语(subject complement)。 在正式英语中，充当谓语主格的代词通常是主格(subjective case)，例如，I, we, he, she and they。而在非正式口语和写作中，这样的代词通常是宾格，例如，me，us, him, her 和them。也有观点认为，如果你认为连系助动词可以作为等价的符号，则跟在它后面的部分就是谓语主格。如果你将谓语主格与主语切换位置，它仍然有意义。谓语主格与“to be”动词连用，其结果就是，回答了“是什么，或者谁在做什么”这样的问题。因此，除了谓语主格是连系助动词的主语，谓语主格可以等价于直接宾语。
1.3 第三种定义
谓语主格(也称为谓语名词)就是一个名词或名词短语，使连系助动词连接完整，并起到重命名主语的作用。（代词当名词看待，即谓语主格必须是名词或名词短语，代词。）
1.4 对以上定义的理解
以上三种定义中，虽然定义的角度稍有偏差，但是都表达了其含义。可以这样理解：所谓谓语主格，从字面意思与其在句子中的角色理解，就是位于谓语之后，名词本身又必须是主格，所以称为谓语主格(即是主语的别名或同等地位)，从这个角度理解比较好理解。
1.5 判断方法和注意事项
(1) 谓语主格不能跟在动作性动词之后，因为唯一能跟在动作性动词之后的名词是充当间接的，或者直接的宾语。
(2) 并非所有跟在连系助动词之后的词汇都是谓语主格，谓语主格始终是名词或代词，并重命名主语。连系助动词分为以下几类：
a. “to be”动词(以各种格式出现，例如，am, are, is, was, were, will be, has been, have been)。
b. 感官动词(“sense”verbs)(例如，to feel, to look, to smell, to taste, to sound，等等)。
c. 状态动词(“status”verbs)，(即相对于动作性动词而言，动词既表示动作，也表示某种发展变化的状态，例如，to appear, to become, to continue, to grow, to seem, to turn，等等)。
你可能已注意到，很多跟在连系助动词之后的词汇是形容词，对主语进行描述或说明，即谓语性形容词(predicate adjective)，即紧跟在谓语之后对主语进行描述的形容词，所以很多语法书上将谓语性形容词译为“表语”有点词不达意，偏离了语法原本的含义，让人匪夷所思，“表”是什么意思？表达？代表？表意？能起表达含义的语份成分太多了，为什么要译成这么外名称？。
下面举几例说明——
· John is brilliant. (John才华横溢。)
brilliant是形容词，因此，是谓语形容词，不是谓语主格。需要注意，谓语主格和谓语形容词都归为主语补语，但是它们不是一样的文法成分。
· It feels great.
great是形容词，因此，是谓语形容词，不是谓语主格。
试比较下面两个句子：
· The sea is dangerous.
形容词dangerous是谓语形容词，不是谓语主格。
· The sea is a danger.
名词 a danger 是谓语主格。
2. 一些例子加深理解
2.1 “to be”动词之后的谓语主格例子，加粗部分表示“to be”动词，斜体部分表示谓语主格
· I am now acting president of the corporation.
· Wind turbines are a renewable source of power.
· Many people's favorite movie genre is action or drama.
· Mario Garcia has been councilman for five years.
· A teenager's favorite food must be hot dogs.
· My homes have been a basement apartment, a trailer, and a house.
· Dinner can be whatever you find in the refrigerator.
· Kathy has been my neighbor since I moved in.
· J. K. Rowling may be one of the best writers ever.
· Rhonda used to be the tallest girl in her class.
· An honest man should have been the leader of the country.
· At the end of the tournament, my daughter was the leader.
· He is a real help to his mother.
· Before the competition, they were the favorites to win.
· Pavarotti was a wonderful tenor.
· BMWs and Mercedes are luxury cars.
· For many of us on the team, the fans were an embarrassment.
· When I was younger, my favorite pastime was reading.
· Neil Armstrong and Buzz Aldrin were the first astronauts to walk in the moon.
2.2 状态动词(非动作动词)之后的谓语主格例子
· You seem upset.
· Why does she appear so upset?
· I would like to remain anonymous.
· The soup smells good.
· Her new song sounds rather sad.
· Her new soup tastes horrific.
· Mary still seemed a queen ( = was a queen in seeming, or appearance ).
2.3 名词短语作谓语主格的例子
· The new law is an opportunity and a risk.
名词短语an opportunity and a risk作为谓语主格。
· I will be your employer, your friend, and your uncle.
名词短语your employer, your friend, and your uncle.作为谓语主格。
2.4 应用谓语主格的名句
· "Today is a king in disguise."
· "We are the world / We are the children / We are the ones who make a brighter day."
— "We Are the World" 由Michael Jackson 和 Lionel Richie所作
· "I am the king of the world!"
— Jack Dawson, Titanic
