English verbs are divided by function into two basic categories: linking verbs and action verbs. Linking verbs are also called being verbs because they express states of being. Action verbs, well, they describe an action. Linking verbs are like giant equal signs plopped into the middle of your sentence.
For example, you can think of the sentence
Ralph’s uncle is a cannibal with a taste for finger food.
as
Ralph's uncle = a cannibal with a taste for finger food.
Or, in shortened form,
Ralph’s uncle = a cannibal
Just as in an algebra equation, the word is links two ideas and says that they are the same. Thus, is is a linking verb. Here are more linking verbs:
Lulu will be angry when she hears about the missing bronze tooth.
Lulu = angry (will be is a linking verb)
Stan was the last surfer to leave the water when the tidal wave approached.
Stan = last surfer (was is a linking verb)
Here are some linking verbs that are not forms of the verb to be:
With his foot-long fingernails and sly smile, Big Foot seemed threatening.
Big Foot = threatening (seemed is a linking verb.)
A jail sentence for the unauthorized use of a comma appears harsh.
jail sentence = harsh (appears is a linking verb in this sentence)
The penalty for making a grammar error remains severe.
penalty = severe (remains is a linking verb in this sentence)
Seemed, appears, remains, and stays are similar to forms of the verb to be in that they express states of being. They simply add shades of meaning to the basic concept. You may, for example, say that
With his foot-long fingernails and sly smile, Big Foot was threatening.
Now the statement is more definite. Seemed leaves room for doubt. Similarly, remains adds a time dimension to the basic expression of being. The sentence implies that the penalty was and still is severe.
Sensory verbs may also be linking verbs:
The ten-year-old lasagna in your refrigerator smells disgusting.
lasagna = disgusting (smells is a linking verb)
The ten-year-old lasagna in your refrigerator also looks disgusting.
lasagna = disgusting (looks is a linking verb)
Needless to say, the ten-year-old lasagna in your refrigerator tastes great!
lasagna = great (tastes is a linking verb)
Verbs that refer to the five senses are linking verbs only if they act as an equal sign in the sentence. If they aren’t equating two ideas, they aren’t linking verbs. In the preceding example sentence about Ralph’s double chin, feel is a linking verb. Here’s a different sentence with the same verb:
With their delicate fingers, Lulu and Stan feel Ralph’s chin.
In this sentence, feel is not a linking verb because you’re not saying that
Lulu and Stan = chin.
Instead, you’re saying that Lulu and Stan don’t believe that Ralph shaved, so they went stubble hunting.
Linking verbs are important, but unless you’re in some sort of hippie commune left over from the sixties, you just can’t sit around being all the time. You have to do something. Here's where action verbs come into the picture. Everything that is not being is action, at least in the verb world. Unlike the giant equal sign associated with linking verbs, something happens with an action verb:
Drew slapped the offending pig right on the snout. (Slapped is an action verb.)
Fred will steal third base as soon as his sneezing fit ends. (Will steal and ends are action verbs.)
According to the teacher, Roger has shot at least 16 spitballs in the last ten minutes. (Has shot is an action verb.)
Don’t let the name action fool you. Some action verbs aren’t particularly energetic: think, sit, stay, have, sleep, dream, and so forth. Besides describing the ideal vacation, these words are also action verbs! Think of the definition this way: if the verb is not a giant equal sign (a linking verb), it’s an action verb.