What Are Subject Complements in English Grammar?

A subject complement is a word or phrase (usually an adjective phrase, noun phrase, or pronoun) that follows a linking verb and describes or renames the subject of the sentence. Also called a subjective complement.

In traditional grammar, a subject complement is usually identified as either a predicate nominative or a predicate adjective.

Examples and Observations

• The light in the chapel was warm and soft.
• Mrs. Rigney was my fourth-grade teacher.
• My fourth-grade teacher was exceptionally kind.
• "Ruth and Thelma are my best friends, and their roomies are Tammy Hinsen and Rebecca Bogner." (Dean Koontz, Lightning. G.P. Putnam's Sons, 1988)
• "I knelt down and pulled on the edge of the stone with him, and it started to move with the sucking sound of thick mud. It smelled awful, and we looked at each other with sour faces." (Patrick Carman, The Land of Elyon: Into the Mist. Scholastic Press, 2007)
• "The Johnson children and Harbor Branch received $169 million. But if they were the true winners, no one was the loser." (Barbara Goldsmith, Johnson V. Johnson. Knopf, 1987)
• "The very air was alive with the uncanny cries of phantoms that flew through the secret places of this region. These mountains were unfriendly at the best of times." (David Bilsborough, The Wanderer's Tale. Tor, 2007)

Linking Verbs and Subject Complements

"If a verb requires a subject complement (SC) to complete the sentence, the verb is a linking verb. The subject complement ([italicized] in the examples that follow) typically identifies or characterizes the person or thing denoted by the subject:

(1) Sandra is my mother's name.
(2) Your room must be the one next to mine.
(3) The upstairs tenant seemed a reliable person.
(4) A university is a community of scholars.
(5) The receptionist seemed very tired.
(6) You should be more careful.
(7) The distinction became ​quite clear.
(8) The corridor is too narrow.

The most common linking verb is be. Other common linking verbs (with examples of subject complements in parentheses) include appear (the best plan), become (my neighbor), seem (obvious), feel (foolish), get (ready), look (cheerful), sound (strange). Subject complements are typically noun phrases, as in (1)-(4) above, or adjective phrases, as in (5)-(8) above." (Gerald C. Nelson and Sidney Greenbaum, An Introduction to English Grammar, 3rd ed. Routledge, 2009)

The Difference Between a Subject Complement and an Object

The Subject Complement is the obligatory constituent which follows a copular verb and which cannot be made the subject in a passive clause:

Who's there? It's me / It's I.*
She became a tennis champion at a very early age.
Feel free to ask questions!

The Subject Complement does not represent a new participant, as an Object does, but completes the predicate by adding information about the subject referent. For this reason, the Subject Complement differs from the Object in that it can be realized not only by a nominal group but also by an adjectival group (Adj.G), as illustrated in the previous examples.

"The objective case (me) is now in general use (It's me) except in the most formal registers, in which the subjective form (It's I) or (I am he/she) are heard, especially in AmE.

"As well as be and seem, a wide range of verbs can be used to link the subject to its Complement; these add meanings of transition (become, get, go, grow, turn) and of perception (sound, smell, look) among others..." (Angela Downing and Philip Locke, English Grammar: A University Course, 2nd ed. Routledge, 2006)

Agreement with Subject Complements

"(16c) These are the costs the grey parties never talk about when they allow the system to go on. (w2b-013:097) . . .
(16h) I call them wild flowers. . . .(s1a-036:205)

"In those cases in which the complements are noun phrases, the subject complement shows concord with the subject S, and the object complement is in concord with the direct object, as can be best seen in the examples (16c) and (16h)." (Rolf Kreyer, Introduction to English Syntax. Peter Lang, 2010)

Semantic Relations

The italicized portions of the following examples are Subject Complements. The upper case labels to the right indicate the semantic relation between the Subject Complement and the Subject:

(4a) The venue for the meeting is the Roxburghe Hotel. EQUATION
(4b) The estate car is a Volvo. PROPER INCLUSION
(4c) You're so young. ATTRIBUTION
(4d) Would you still love me if I were old and saggy? ATTRIBUTION
(4e) that telly was mine POSSESSION
(4f) Sometimes we're on a collision course, LOCATION
(4g) the NHS was for all of us BENEFACTEE
(4h) The five pound note was for services rendered. IN EXCHANGE

The Inflection (marking for tense, aspect, mode, and agreement) in this type of construction is carried by be; therefore be is the syntactic Head of the Predicate. However, the Subject Complement is the element that expresses the main semantic content of the Predicate. In other words, the Complement is the semantic Head of the Predicate."

Source

Thomas E. Payne, Understanding English Grammar: A Linguistic Introduction. Cambridge University Press, 2011