A gerund phrase is a phrase consisting of a gerund and any modifiers or objects associated with it. A gerund is a noun made from a verb root plus ing (a present participle). A whole gerund phrase functions in a sentence just like a noun, and can act as a subject, an object, or a predicate nominative.
If you look up the definition of gerund (pronounced JER-und), you will find that it means “an English noun formed from a verb by adding -ing”; that is, a present participle used as a noun.
My passion is reading.
My doctor suggests running to improve my health.
In all three of these examples, words ending with -ing are acting as nouns. Traveling is the subject of the first sentence. In the second sentence, reading is a predicate nominative, a word (or group of words) that completes a linking verb and renames the subject. The verb is, a form of the linking verb to be, is followed by reading, which renames the subject my passion. In the third sentence, the gerund running is acting as the object of the verb suggests.
How Do Gerund Phrases Work? They Act Like a Noun
Gerunds can appear alone or band together with other words to form a gerund phrase. Collectively, this phrase behaves like a single noun.
Running with scissors is a favorite activity of mine.
Both the gerund and the gerund phrase above function as subject nouns and take the third-person singular verb is. We could substitute a non-gerund noun such as chess to mentally confirm its function.
Not Acting Like a Noun? It’s a Participle Phrase
Gerund phrases can easily be confused with participle phrases. It is possible, for example, to encounter the gerund phrase we used above in a context where it is not acting like a noun. When used as a modifier—that is, as an adjective or adverb—it is now a participle phrase.
Here, running with scissors modifies the verb charged. It gives us further information about how Tim charged.
Gerund Phrases as Objects
Just as nouns sometimes function as objects in a sentence, so can gerund phrases.
In this sentence, the gerund phrase running with scissors is the direct object of the verb enjoys. We could easily replace it with a simpler object noun to confirm that it really is an object.
(That would be a much better idea, Tim.)
We could also use this gerund phrase as an indirect object.
Like many indirect objects, the gerund phrase running with scissors is introduced with the preposition to.
You may have heard of dangling participles; dangling gerunds are quite similar. Dangling gerunds are somewhat less frequent, but they can crop up when gerunds or gerund phrases are acting as objects of a preposition such as before, after, by, or with.
The gerund phrase is said to be dangling here, because it is mismatched with the subject that follows, creating an illogical scenario. The writer of a such a sentence no doubt intended to convey that when Tim ran with scissors, his cat was injured. But as the sentence reads, it is the (atypically scary) cat who ran with scissors.
The best thing to do with a sentence that contains a dangler is to rewrite it to give the sentence its proper subject. There may be a number of ways to do that correctly.