"Running" is usually an example of a verb, but it isn't always. Verbs can function as verbals in sentences and take on other roles. A gerund is a verbal that is created by adding an -ing ending to an action verb. Then the gerund can be placed in the sentence as a noun would be. Words liking "hiking," "sleeping," and "singing" can serve as subjects, objects, and predicate nouns. For example, "Hiking is my favorite pastime" features hiking as the subject. In the sentence, "Maria won the competition by singing a nursery rhyme song," singing is the object of the preposition "by."
Gerunds as Predicate Nouns
Serving as a predicate noun is one of a gerund's important functions. A predicate noun, also known as a subject complement, occurs at the end of a sentence containing a linking verb. The predicate noun renames the subject of the sentence. In the sentence "Cheese is my favorite food," the word "food" is the predicate noun. Gerunds can easily take the place of a predicate noun. In the sentence, "My favorite activity is reading," "reading" is a gerund made by adding -ing to the action verb "read," and it renames the subject of the sentence, which is "activity."