In what part of speech does a verb end in "ing" to operate as a noun, such as "eating breakfast" or "answering the phone" or "walking on the moon"?

When a verb adopts an "-ing" ending but operates within a sentence as a noun, such as in phrases like "eating breakfast" or "answering the phone," it is performing a distinct grammatical function. This transformation allows an action to become the subject, object, or complement of a sentence, rather than simply describing an action being carried out.

This specific part of speech is called a gerund. A gerund consistently ends in "-ing" and functions precisely like a noun. For example, in the phrase "walking on the moon," "walking" acts as the noun representing the activity itself. Similarly, if someone says "I enjoy swimming," "swimming" serves as the direct object of the verb "enjoy," demonstrating its noun-like behavior. Gerunds can also follow prepositions, as seen in "She is skilled at painting."

It's crucial to differentiate gerunds from present participles, which also end in "-ing." While gerunds serve as nouns, present participles function differently; they either act as adjectives, as in "the barking dog," or form part of continuous verb tenses, such as "He is studying." The context and role of the "-ing" word within the sentence are key to identifying whether it is a gerund or a present participle. Understanding this distinction highlights the versatility of verb forms in English.

The capacity for a verb to assume a noun's role through the gerund form significantly enhances the flexibility and conciseness of English sentence construction. This grammatical tool allows speakers and writers to treat actions as concrete concepts, making communication more efficient and nuanced.