What Is a Copula Verb?

In English grammar, a copula is a verb that joins the subject of a sentence or clause to a subject complement. For example, the word is functions as a copula in the sentences "Jane is my friend" and "Jane is friendly."

Adjective: copular. Pronunciation: KOP-u-la. Also known as a copular verb or a linking verb. Contrast with a lexical verb and a dynamic verb.

The primary verb be is sometimes referred to as "the copula." However, while forms of being (am, are, is, was, were) are the most commonly used copulas in English, certain other verbs (identified below) have copular functions as well. 

Unlike auxiliary verbs (also called helping verbs), which are used in front of other verbs, copular verbs function by themselves in the manner of main verbs.

See Examples and Observations below. Also, see:

• Ascriptive Sentence
• Double Copula
• Linking Verb
• Stative Verb
• Verb of Being
• Zero Copula

From the Latin, "link"

• "These two very old people are the father and mother of Mr. Bucket. Their names are Grandpa Joe and Grandma Josephine."
  (Roald Dahl, Charlie and the Chocolate Factory, 1964)
• The weather is horrible.
• That car looks fast.
• The stew smells good.
• I do feel a fool.
• She became a racehorse trainer.
• It's getting late.
• He spoke intelligently. (Intelligently is an adverb. It tells you about how the person spoke.)
• He looks intelligent. (Intelligent is an adjective in a predicative position. It tells you about the person himself--rather like saying 'He is intelligent.' The look is a copular verb.)
• Common Copulas
  "We use a special kind of verb to join an adjective or noun complement to a subject. These verbs can be called 'copulas' or 'copular verbs.' Common copular verbs are: be, seem, appear, look, sound, smell, taste, feel, become, get."After copular verbs, we use adjectives, not adverbs. Compare: "Note that some of these verbs are also used with other meanings as ordinary non-copular verbs."
  (Michael Swan, Practical English Usage. Oxford University Press, 1995)
  "A copular (or linking) verb is complemented by a subject predicative in a sentence or clause structure. The most common copular verb is; others include become (my friend), feel (tired), get (ready), seem (happy). A copular prepositional verb is a prepositional verb (combination of a verb plus preposition) that is complemented by a subject predicative: sound like (you), turn into (a monster), serve as (mitigating circumstances)."
  (Sidney Greenbaum, Oxford English Grammar. Oxford University Press, 1996)