1. The classification of English verbs (英语动词的分类)

		及物动词 (transitive verb, vt)
	主动词 (main verb) = lexical verb (实义动词, 实意动词, 词汇动词) = 完全动词 (full verb)	不及物动词 (intransitive verb, vi)
		系动词 (copula, copular verb, copulative) = 连系动词 (linking verb)
动词 (verb)
		基本助动词 (primary auxiliary)
	助动词 (auxiliary verb) = 辅助动词 (helping verb, helper verb)	情态助动词 (modal auxiliary)
		半助动词 (semi-auxiliary)

2. 系动词 (连系动词)

The word copula derives from the Latin noun for a link or tie that connects two different things.

copula /ˈkɒpjələ/：n. 连系动词
linking verb /ˈlɪŋkɪŋ vɜːb/：n. 系词，连系动词

A copula is often called a linking verb.
系动词 (连系动词) 是谓语动词，用于连接主语和表语。

系动词 (连系动词) 没有被动语态。

系动词本身有词义，但不表示具体的动作，而只是起连接主语和后面成分的作用。系动词后面所接的成分是用来说明主语的特点，表明主语的性质、状态、特征等，可以称之为主语补足语或表语。

系动词本身有词义，但不能单独用作谓语部分，须后接表语 (又称为主语补足语) 构成系表结构的谓语部分。

• Cambridge Dictionary

copula /ˈkɒp.jə.lə/: noun 系动词

a type of verb, of which the most common is “be”, that joins the subject of the verb with a complement:
In the sentence “You smell nice”, “smell” is a copula.
在 You smell nice 这句话中，smell 是系动词。

linking verb /ˈlɪŋ.kɪŋ ˌvɜːb/: noun 系动词，连系动词

a verb that connects the qualities of an object or person to that object or person:
In the sentence “My bags weigh 45 kg”, “weigh” is a linking verb.
在句子 My bags weigh 45kg 中，weigh 是系动词。

• Longman Dictionary of Contemporary English

copula: noun [countable]
linking verb: noun [countable]

a type of verb that connects the subject of a sentence to its complement, for example “seem” in the sentence “The house seems big” SYN linking verb

2.1. Grammatical function (语法功能)

A copula is a word or phrase that links the subject of a sentence to a subject complement, such as the word “is” in the sentence “The sky is blue” or the phrase “was not being” in the sentence “It was not being cooperative.”
连系动词 (系动词) 是连接句子主语和主语补足语的词或短语。

A linking verb is a verb that describes the subject by connecting it to a predicate adjective or predicate noun (collectively known as subject complements).

cooperative /kəʊˈɒpərətɪv/：adj. 合作的，配合的，协作的，协助的，同心协力的，共同拥有共同经营利益共享的 n. 合作企业，合作社组织
latin /ˈlætɪn/：n. 拉丁语，拉丁人 adj. 拉丁语的，拉丁人的，用拉丁语写成的

The principal use of a copula is to link the subject of a clause to a subject complement. A copular verb is often considered to be part of the predicate, the remainder being called a predicative expression.
系动词用于将主语与主语补足语连接起来，系动词是谓语动词。

A simple clause containing a copula is illustrated below:

The book is on the table.

In that sentence, the noun phrase “the book” is the subject, the verb “is” serves as the copula, and the prepositional phrase “on the table” is the predicative expression.
名词短语 the book 是主语，谓语动词 is 是系动词，介词短语 on the table 是表语。

The predicative expression accompanying the copula, also known as the complement of the copula, may take any of several possible forms: it may be a noun or noun phrase, an adjective or adjective phrase, a prepositional phrase (as above), or an adverb or another adverbial phrase expressing time or location.

accompany /əˈkʌmpəni/：vt. 伴随，陪同，陪伴，为 ... 伴奏，与 ... 同时发生
adverbial [ədˈvɜː(r)biəl]：adj. 副词的，状语的 n. 副词类

Examples are given below, with the copula in red and the predicative expression in blue.
系动词以红色表示，表语以蓝色表示。

Mary and John are my friends.
The sky was blue.
I am taller than most people.
The birds and the beasts were there.

3. 表语和主语补足语

中国的语法学家称作表语的部分，西方的语法学家称为主语补足语 (subject complement)。国外的语法学家对于主语补足语 (subject complement) 定义的范围很大，不利于把握，因而国内的语法学家把这些称为表语，这样划分更简洁，对学习更有利。

传统语法把系动词后的成分称为表语，现代语法把系动词后的成分称为主语补足语。

补足语 (complement) 是一种补足主语或宾语意义的句子成分。补足主语意义的句子成分叫做主语补足语 (subject complement)，补足宾语意义的句子成分叫做宾语补足语 (object complement)。

3.1. Predicative expression (表语)

表语用于表示主语的特征，起表示、说明的功能。

predicative /prɪˈdɪk.ə.tɪv/: adjective 作表语的，谓语性的

• Cambridge Dictionary

(in grammar, especially of adjectives or phrases) following a verb:
In the sentence “She is happy”, “happy” is a predicative adjective.
In the sentence “I was sad”, “sad” is a predicative adjective.

• Longman Dictionary of Contemporary English

A predicative adjective or phrase comes after a verb, for example “happy” in the sentence “She is happy”.

A predicative expression (or predicative) is part of a clause predicate, and is an expression that typically follows a copula or linking verb, e.g. be, seem, appear, or that appears as a second complement of a certain type of verb, e.g. call, make, name, etc.

The most frequently acknowledged types of predicative expressions are predicative adjectives (also predicate adjectives) and predicative nominals (also predicate nominals).

predicative adjective：表语形容词，形容词作表语
predicate adjective：谓语性形容词
predicative nominal：表语名词，名词作表语
predicate nominal：谓语性名词

• The man is friendly. (predicative adjective 形容词作表语)

• Bob is a postman. (predicative nominal 名词作表语)

• The snake is in the bag. (predicative prepositional phrase 介词短语作表语)

• That is when it happens. (predicative clause 从句作表语/表语从句)

• It is soon. (predicative adverb 副词作表语)

3.2. Subject complement (主语补足语)

A subject complement is a predicative expression that follows a copula (commonly known as a linking verb), which complements the subject of a clause by means of characterization that completes the meaning of the subject.

When a noun, noun phrase, or pronoun functions as a subject complement, it is called a predicative nominal.
当名词、名词短语或代词充当主语补足语时，它被称为名词作表语。

• The lake was a tranquil pool. (predicative nominal 名词作表语)

Here, was is a copula that links the subject complement a tranquil pool (which has the head noun pool), to the subject the lake (which has the head noun lake).
was 是系动词，它将主语补足语 a tranquil pool (其中心名词为 pool) 与主语 the lake (其中心名词为 lake) 连接起来。

When an adjective or analogous phrase functions as subject complement, it is called a predicative adjective.
当形容词或类似短语充当主语补足语时，它被称为形容词作表语。

• The lake is tranquil. (predicative adjective 形容词作表语)

tranquil /ˈtræŋkwɪl/：adj. 宁静的，安宁的，平静的，安静的

tranquil is a predicative adjective linked to the subject the lake via the copula is.

• That is what I think. (predicative clause 从句作表语/表语从句)

4. Copula-like words

系动词是一种句法功能分类，它的功能是用来体现主语和主语补足语之间的关系，在合适的语境条件下，非常多的动词都可以作为系动词来使用。

Sometimes, the term copula is taken to include not only a language’s equivalent(s) to the verb “be” but also other verbs or forms that serve to link a subject to a predicative expression (while adding semantic content of their own).
系动词不仅包括动词 “be” 的变体，还包括用于将主语与表语联系起来的其他动词或形式 (同时添加它们自己的语义内容)。

For example, English verbs like become, get, feel, look, taste, smell, and seem can have this function, as in the following sentences (the predicative expression, the complement of the verb, is in blue).

She became a student.
They look tired.
The milk tastes bad.
That bread smells good.
I feel bad that she can’t come with us.

These extra copulas are sometimes called “semi-copulas” or “pseudo-copulas.”
它们被称为半系词 (semi-copulas) 或准系词 (pseudo-copulas)。

4.1. List of English copulae

Some main verbs are called linking verbs (or copular verbs). These verbs are not followed by objects. Instead, they are followed by phrases which give extra information about the subject (e.g. noun phrases, adjective phrases, adverb phrases or prepositional phrases).
这些动词后面不跟宾语。相反，它们后面跟的是提供有关主语的额外信息的短语 (例如名词短语、形容词短语、副词短语或介词短语)。

英语的系动词 be 有八种形式：is, was, are, were, be, been, being, am。

• look

Tom looks upset.

• seem

Tom seems happy.

• smell

Tom smelled sweet.

• act

Tom acted suspicious.

• appear

Tom appears satisfied, but really is not.

• be

Tom is a coward.

• become (inchoative)

Tom became wealthy.

• call in

Tom called in sick.

• come

The prediction came true.

• come out

It came out burnt.

• constitute

Verbs constitute one of the main word classes in the English language.

• die

He died poor.

• eat

Tom eats healthy.

• emerge

Tom emerged unharmed after the incident.

• end up

I ended up broke.

• equal

Two plus two equals four.

• get (inchoative)

Tom got angry.

• go

The man went crazy.

• grow (inchoative)

Tom grew insistent.

• fall

Tom fell ill with the flu.

• feel

Tom felt nauseated.

• freeze

The lake froze solid.

• keep

Tom kept quiet.

• lean

This area leans conservative.

• play

The possum played dead.

• prove

Tom’s behavior proves difficult to understand.

• remain

Tom remained unsatisfied.

• run

• shine

Her smile shines bright.

• sound

Tom sounded obnoxious.

• stay

Tom stayed happy.

• take

Tom took ill.

• taste

The food tastes fresh.

• turn (inchoative)

Tom turned angry.

• turn up

Tom turned up missing.

• wax (inchoative)

Tom waxed lyrical.

inchoative /ɪnˈkəʊətɪv/：adj. 表始的 (表示动作自动开始的) n. 表示开始的动词

5. 主语 + 系动词 (谓语动词) + 表语 (主语补足语)

Subject + Linking Verb + Subject Complement

系动词 (又称为连系动词) 不表示具体的动作，而只是起连接主语和后面成分的作用。系动词后面所接的成分是用来说明主语的特点，表明主语的性质特征，因此称之为主语补足语或表语 (能表示主语特征的成分)。

在主谓宾结构中，主语和宾语是由于谓语动词的存在，才有了关系，它们原本无关。

在主系表结构中，表语本来就是主语的补充描述，即使没有系动词的存在，它们也有关。

References

[1] Yongqiang Cheng, https://yongqiang.blog.csdn.net/
[2] List of English copulae, https://en.wikipedia.org/wiki/List_of_English_copulae