Linking verbs do not express action. Instead, they connect the subject of the verb to additional information about the subject. Look at the examples below:
Keila is a shopaholic.
Ising isn’t something that Keila can do. Is connects the subject, Keila, to additional information about her, that she will soon have a huge credit card bill to pay.
During the afternoon, my cats are content to nap on the couch.
Areing isn’t something that cats can do. Are is connecting the subject, cats, to something said about them, that they enjoy sleeping on the furniture.
A ten-item quiz seems impossibly long after a night of no studying.
Seems connects the subject, a ten-item quiz, with something said about it, that its difficulty depends on preparation, not length.
The following verbs are true linking verbs: any form of the verb be [am, is, are, was, were, has been, are being, might have been, etc.], become, and seem. These true linking verbs are always linking verbs.
Then you have a list of verbs with multiple personalities: appear, feel, grow, look, prove, remain, smell, sound, taste, and turn. Sometimes these verbs are linking verbs; sometimes they are action verbs.
How do you tell when they are action verbs and when they are linking verbs?
If you can substitute am, is, or are and the sentence still sounds logical, you have a linking verb on your hands.
If, after the substitution, the sentence makes no sense, you are dealing with an action verb instead. Here are some examples:
Sylvia tasted the spicy squid eyeball stew.
Sylvia is the stew? I don’t think so! Tasted, therefore, is an action verb in this sentence, something Sylvia is doing.
The squid eyeball stew tasted good.
The stew is good? You bet. Make your own!
I smell the delicious aroma of a mushroom and papaya pizza baking in the oven.
I am the aroma? No way! Smell, in this sentence, is an action verb, something I am doing.
The mushroom and papaya pizza smells heavenly.
The pizza is heavenly? Definitely! Try a slice!
My dog Oreo feels depressed after seven straight days of rain.
Oreo is depressed? Without a doubt! Oreo hates the wet.
This substitution will not work for appear. With appear, you have to analyze the function of the verb.
Swooping out of the clear blue sky, the blue jay appeared on the branch.
Appear is something a blue jay can do—especially when food is near.
The blue jay appeared happy to see the bird feeder.
Here, appeared is connecting the subject, the blue jay, to its state of mind, happiness.