Q: In my ESL class, I wrote the following sentence: “I was sick yesterday, so all I did was resting at home.” My teacher said I should have written “rest,” not “resting,” but he couldn’t give a grammatical explanation. He said his native ear informed him. Was he correct?
A: Your teacher was right. That construction calls for an infinitive, “rest,” as a direct object, not a gerund.
He was also right in saying that there’s no good explanation why some verbs take a gerund as a direct object, some take an infinitive, and some take both, as we wrote on our blog in 2010 and 2014. The only way to know which take what is through experience.
As you already know, an infinitive is the bare form of a verb (like “rest”), while a gerund is the infinitive plus “-ing” (“resting”).
Because infinitives and gerunds can act as nouns, they can be the direct objects of verbs. Some verbs (“learn,” “like,” and “prefer,” among others) can have both infinitives and gerunds as direct objects.
For instance, one can say either “I learned to knit” (infinitive) or “I learned knitting” (gerund) … “I like to read” or “I like reading” … “I prefer to rest at home” or “I prefer resting at home.”
But other verbs—“decide” and “finish” are examples—take either one or the other: “She decided to go” (not “She decided going”) … “He finished dressing” (not “He finished to dress”).
When the verb is a form of “to be,” the story varies. Sometimes the direct object is an infinitive, sometimes a gerund, and sometimes they’re interchangeable.
For example, we say, “What he did was walk” (bare infinitive), not “What he did was walking.” But we also say, “His hobby is skiing,” not “His hobby is to ski.” And we can say either “Her passion is vacationing in Tahiti” or “Her passion is to vacation in Tahiti.”
So the verb “to be” is unpredictable, which is why that sentence was mysterious to you and why even linguists have never cracked the code (if there is one).
In case you’re interested, we wrote posts in 2017 that discussed the use of infinitives versus gerunds after “interested” and after “intend.” You can find other relevant posts by putting the words “infinitive” and “gerund” in the search box of our blog and clicking the magnifying glass.