How to use gerunds and infinitives in English?

1. What is a gerund?

A gerund is a verb ending in "-ing" and serves as a noun in sentences (running, swimming, reading). Do not confound gerunds with present participles. They both have the same form, but they have different functions. While gerunds act as nouns, present participles come after a verb to indicate ongoing or continuous actions. Unlike gerunds, present participles can act as adjectives or verbs. For example, in the sentence "The audience enjoyed the thrilling movie last night.", thrilling acts as an adjective and modifies the noun movie. Thus, it is a present participle.

2. What is an infinitive?

An infinitive is a verb’s base form preceded by to (to run, to swim, to read). However, infinitives do not act as verbs and sentences containing them must include at least one conjugated verb. To form negative infinitives, we put not in front of them (not to smoke, not to ignore, not to swim).

1. Do you want to eat anything?
2. Let's go to swim.
3. I really want you not to stay there anymore.
4. We are here to help you.

Both gerunds and infinitives can act as a sentence’s subject or object. These forms of verbs, known as verbals, can be accompanied by modifiers, objects, and complements, creating verbal phrases.

3. Gerunds and infinitives rules

3.1. Verb + preposition + gerund

Do not use an infinitive if a verb is followed by a preposition.

Examples:

3.2. Verb + gerund or infinitive with little or no change in meaning

Some verbs can be followed by either a gerund or an infinitive with little or no change in meaning:

3.3. Verb + gerund or infinitive with no change in meaning but different structure

The verbs allow, permit, advise, encourage, and forbid can be followed by either a gerund or an infinitive but require a change of structure.

1. Gerund: Verb + "ing"
2. Infinitive: Verb + object + infinitive

3.4. Verb + gerund or infinitive with a change in meaning

Some verbs can be followed by either a gerund or an infinitive, but the meaning changes.

1. stop:
1. He stopped smoking. (He quit smoking.)
2. He stopped to smoke. (He stopped what he was doing in order to smoke.)
2. remember:
1. I remember turning off the oven before I left. (You recall what you did. You recall that you turned off the oven before leaving.)
2. Remember to turn off the oven before you leave. (Don't forget to turn off the oven before you leave.)
3. I remembered to turn off the oven before I left. (First, you remembered that you had to turn off the oven before leaving. Then, you turned off the oven.)
3. forget:
1. I'll never forget being single for such a long time. ( You didn't recall turning off the light. You are not sure if you turned off the light or not.)
2. I forgot to turn off the light. (First you forgot, then you did not turn off the light. Thus, the light was not turned off.)
4. regret:
1. I regretted being rude to her. (I wish I was not rude to her.)
2. I regret to inform you about the passing of our beloved one. (First you regret, then you inform the passing of your beloved one. You feel sorrow about what you are about to say.)

3.5. Gerunds and infinitives as subjects

When gerunds and infinitives function as the subject of a sentence, they are followed by a singular verb. However, when they are linked by and, they take the plural form of the verb.

1. Swimming is a healthy exercise.
2. Gardening provides many health benefits.
3. Swimming and gardening are examples of two healthy recreational activities.
4. To listen is the first step towards empathy.

You can add more context to your writing by including some words after the gerunds or infinitives. For example, Feeding the birds is strictly prohibited. In this sentence, Feeding the birds is a gerund phrase which acts as the subject of the sentence and gives more clarification on what is being prohibited. See more examples below.

1. Swimming in the river is forbidden. 
2. To not trust your partner can be detrimental to your relationship.
3. Shopping in this mall is really enjoyable.
4. To build a strong relationship requires mutual respect and understanding.

3.6. Gerunds and infinitives as objects

Gerunds and infinitives can function as the objects of a sentence.

1. I hate smoking.
2. My parents love hiking.
3. I want to smoke.
4. We need to go.

Here also you can be more specific by adding any modifiers or complements after the gerunds or infinitives.  He admitted killing his wife. In this sentence, killing his wife is a gerund phrase which clarifies who was being killed.  

1. My parents love hiking the Table Mountain in Cape Town.
2. You need to update your computer.
3. She enjoys reading mystery novels.
4. I learned to play the guitar over the summer.
5. He agreed to help us move next weekend.

We do not use an infinitive if a verb is followed by a preposition.

4. Common verbs followed by gerunds

5. Common verbs followed by infinitives

6. Adjective + infinitive

Certain adjectives are followed by an infinitive using the structure "Subject + be + adjective + infinitive". Here are some common examples:

7. Noun + infinitive

Some nouns are followed by an infinitive to show purpose or intent. Here are some common examples:

8. External ressources

1. Verb + Infinitive with change in meaning
2. Gerund + infinitive with no change in meaning
3. Common verbs followed by infinitives
4. Gerund or infinitive. In this video, Lucy explains in details when to use gerunds and infinitives.