Linking verbs show equality by connecting the items that are equal. For instance, if you look at the sentence, "Tara is beautiful." You could substitute the equal sign for "is" and make it "Tara = beautiful," because in the sentence it equates the person Tara with beauty. The same idea works with sentences like "The car is loud" or "The frog is green." In the first sentence the car equals loud, and in the second sentence the frog equals green. If you left out the linking verb it wouldn't make sense. "The car loud" or "Frog green" make very little sense without the linking verb.
Linking verbs sometimes show a change to a different state or place. When a person says phrases like, "became stormy," "has turned," or "is moving," the linking verb shows a change happening. Look at these examples: "The sky became dark," "The storm has moved far away." The linking verb "became" in the first sentence shows change, and the linking verb "has" in the second sentence shows a change of place.
Predicate nouns replace or rename the subject of the sentence. For instance, in the following sentence the subject of the sentence is rat. "The rat is a furry little beast." In the sentence, the word "beast" renames the rat in the predicate, and the words furry and little both modify the word beast. In the sentence, "Mike is a big bully," Mike is the subject, and bully renames Mike in the predicate. The word "big" modifies the word bully, so you know more about the predicate noun.
Predicate adjectives describe the subject in the sentence. In the sentence, "The dogs were hungry," "hungry" is the predicate adjective. The predicate adjective describes the subject. Another example of predicate adjectives is in the following sentence: "My book is big, heavy and cool." "Big," "heavy" and "cool" all describe the book in the subject of the sentence. Sentences sometimes contain predicate adjectives and predicate nouns. In the sentence, "The rat is a furry little beast," "beast" is the predicate noun, and "furry" and "little" are both predicate adjectives.