Linking Verb

A linking verb is a verb that connects the subject of a sentence to the complement. It is sometimes called a copula or a copular verb. An example is the word is in the sentence "The sky is blue".

Introduction to the term

The linking verb essentially connects a noun with a phrase that describes the nature or quality of that noun. In English, the most common linking verb is simply "be". Others include the verbs that describe the five physical senses. 

Linking Verb - Correct usage

For your reference, here is an example of the linking verb being used correctly in a sentence. 

"The color of the flower was extremely vivid, due to the fact that it had been warm and rainy for the last several days." 

In this sentence, "was" is a linking verb connecting the noun "color" with the description "vivid". 

Now, here is an example of the linking verb being used incorrectly in a sentence. 

"The runner was going to the park in order to train for the marathon that was coming up in a couple months."

Although this sentence is grammatically correct, "was" is actually a helping verb and not a linking verb, because it is followed by a verb (going) and not a descriptive phrase. 

Here are a couple rules you can follow in order to make sure you're using the linking verb in a proper way. 

1. The linking verb is always used by itself. This makes it different from the helping verb, which precedes another verb. The linking verb is generally the only verb in its clause, and it connects the noun not with another verb but rather with a descriptive phrase consisting of other nouns and/or adjectives. 
2. In general, you just use the linking verb in order to say how something was, or how you sensorily experienced something. For example, you may say that the movie was boring, or that he girl smelled good, or that a given man was mayor. The purpose of the linking verb is simply to allow you to make such statements about the properties or qualities of a given noun. 

Linking verbs linked to human need

The linking verb clearly has its origins in the basic need of people to describe the objects around them in a simple and coherent way. For example, one can almost imagine a primitive person (like the pre-Revolutionary Native Americans) needing to tell his tribe that "the bear was big". People need to understand the qualities of the objects around them, so that they can then figure out how they should feel about those objects and then plan their actions accordingly. This is the basic pragmatic function that is fulfilled by the linking verb. 

This also means that the linking verb does not generally fulfill the kind of function most people expect of most verbs: that is, it does not describe an action of some kind, per se. Or, it only does so insofar as occupying a certain state of being can itself can be called an action. For example, to say that the "man was hungry" could be interpreted to mean "the man was being hungry". The latter, though, would be grammatically incorrect. Given its function, the linking verb thus ends up being used in some of the simplest sentences possible in the English language.