Infinitives are verbs in the to 1 verb form (to write, to read, to go); gerunds are verbs that end in -ing and act as subjects or objects within a sentence. In general, infinitives tend to indicate intentions, desires, or expectations, and gerunds tend to state facts. Knowing whether to use a to form or an -ing form in a particular sentence can be a challenge. Though no simple explanation will make it an easy task, some hints might be helpful (see 56d for another strategy).

My adviser urged me to apply to several colleges.

Applying took a great deal of time.

In the first sentence, to apply conveys the message that the act of applying was something wanted, not yet a fact. In the second sentence, applying calls attention to the fact that the application process was actually carried out.

Using infinitives (to forms) to state intentions

Kumar expected to get a good job after graduation.

Last year, Fatima decided to become a math major.

The strikers have agreed to go back to work.

At the moment indicated by the verbs expect, decide, and agree in these sentences, those actions or events were merely intentions. These three verbs, as well as many others that specify intentions (or negative intentions, such as refuse), must always be followed by an infinitive, never by a gerund. Many learner dictionaries provide information about verbs that must be followed by an infinitive instead of a gerund.

Using gerunds (-ing forms) to state facts

Jerzy enjoys going to the theater.

We resumed working after our coffee break.

Kim appreciated getting candy from Sean.

In all of these cases, the gerund indicates that the action or event that it expresses has actually occurred. Verbs like enjoy, resume, and appreciate can be followed only by gerunds, not by infinitives. In fact, even when these verbs do not convey clear facts, the verb form that follows must still be a gerund. Again, many dictionaries provide this information.

Kim would appreciate getting candy from Sean, but he hardly knows her.

Understanding other rules and guidelines

A few verbs can be followed by either an infinitive or a gerund. With some, such as begin and continue, the choice makes little difference in meaning. With others, however, the difference in meaning is striking.

Carlos was working as a medical technician, but he stopped to study English.

The infinitive to study indicates that Carlos intended to study English when he left his job. We don’t know whether he actually did study English.

Carlos stopped studying English when he left the United States.

The gerund studying indicates that Carlos actually did study English but then stopped when he left.

The distinction between fact and intention is not a rule but only a tendency, and it can be outweighed by other rules. For example, use a gerund—never an infinitive—right after a preposition.

For a full list of verbs that can be followed by an infinitive and verbs that can be followed by a gerund, see Grammar Troublespots, Third Edition, by Ann Raimes (Cambridge UP, 2004), or Cambridge International Dictionary of English (Cambridge UP, 1999).