Linking verbs do not express action. Instead, linking verbs express a state of being. So, you have action verbs and linking verbs. And so, linking verbs are reserved for expressing a state of being.
So, an example is: “John was a doctor.”
“Was” here is a linking verb, and it’s expressing a state of being, John being a doctor.
And then, “the grapefruit” here “is too sour“.
“The grapefruit is too sour.”
So, “is” is the linking verb here, and again, it’s expressing a state of being, because it’s describing “grapefruit“.
So, in addition to “was” and “is“, some other linking verbs are “am“, “are“, “were“, “be“, “being“, and “been“.
Now, a noun or an adjective is going to follow a linking verb.
So, when an adjective follows a linking verb, it describes the subject.
So, an example is:
“This fruit is mushy.”
So, we already know that “is” is the linking verb. And so, we look at the word following the linking verb, and we know it has to be a noun or an adjective. And we know that “mushy” is an adjective, and so it must be describing the subject. And, sure enough, “mushy” is describing the subject, which is “fruit“.
Now, when a noun follows a linking verb, it renames the subject.
So, here we have:
“He is a doctor.”
Again, the linking verb is “is“, and so, the word following it is “doctor“. And so, we know that “doctor” is a noun, so it must be renaming the subject. And, sure enough, it is, because “doctor” and “He” are interchangeable here, because they’re referring to the same person.
Now, some sense-related verbs can also act as linking verbs, such as “feel“, “look“, “smell“, “sound“, and “taste“.
And then, there are some other verbs in general that can sometimes act as linking verbs, like “appear“, “become“, “grow“, and “seem“.
And so, we have some verbs that can be either an action verb or a linking verb, depending on their meaning in a sentence.
Some examples are “appear“, “become“, “feel“, “grow“, “look“, “smell“, “sound“, and “taste“.
So, right here, we’re using the verb “grew“. So, here’s an example of it as a linking verb.
“Mary grew ill.”
And so, a linking verb, it’s going to have a noun or an adjective following it, so here we have “ill“, which is an adjective. And so, since it’s an adjective, it must be describing the subject. And, sure enough, it is, it’s describing “Mary“. It’s saying that Mary is ill.
Right here, we have an action verb.
“We grew tomatoes.”
It’s the same word, but this time, it’s acting as an action verb.
Now, pretend for a second that it is a linking verb. We look at the word “tomatoes“, and we see that it’s a noun, so it must be renaming the subject. Well, “We” and “tomatoes” aren’t interchangeable, because “We” and “tomatoes” are not the same thing. So, we know that “grew” here must be an action verb.
So, you just have to base-off the context of a sentence when you’re trying to decide whether a verb is acting as a linking verb or an action verb.
But, when you come up to these words up here, these verbs are always going to be linking verbs. But, when you come to sense-related verbs, as well as some other verbs, they can act as a linking or action verb.