A linking verb is one that assists in the renaming or describing of a subject or direct object in a sentence.
One can identify a linking verb by thinking in terms of equality. If the subject or direct object is equal to the subject complement or object complement, respectively, then the verb is a linking verb.
The most frequently used and easiest to identify of these verbs is some conjugation of "to be." Others are commonly verbs dealing with perception ("looks," "sounds," "smells," etc).
Some examples of linking verbs in action:
- Zim is green.
- GIR seems "not good."
In both of those, one could stick an equals sign (sometimes one, sometimes two, depending on whether you're a pedantic programmer or not) where the linking verb is.
If the sentence has a linking verb describing its subject, a subject complement follows the linking verb. If the sentence has a linking verb describing a direct object, an object complement follows the direct object.