When a verb ends in -ing, it may be a gerund or a present participle. It is important to understand that they are not the same.
When we use a verb in – ing form more like a noun, it is usually a gerund.
Reading is fun.
When we use a verb in -ing form more like a verb or an adjective, it is usually a present participle.
Tomas is reading.
We have a boring teacher.
We use them as nouns, so gerunds can be the subject, object or complement of a sentence.
Smoking is bad for your health.
I like travelling.
My favourite pastime is reading.
But, like a verb, a gerund can also have an object itself. In this case, the whole expression (gerund + object) can be the subject, object or complement of the sentence.
Smoking cigarettes is bad for your health.
I like travelling by train.
My favourite pastime is reading science fiction books.
If we want to use a verb after a preposition, it must be a gerund. It is impossible to use an infinitive after a preposition.
I am looking forward to hearing from you.
Martha always dreams about going on holiday.
Please lock the door before leaving.
We usually use gerunds after the verbs like, love, dislike, hate, enjoy, prefer.
They enjoy spending weekends in the country.
We also use gerunds after the verbs start, begin, stop, finish.
Will you please stop talking?
We use gerunds after the verb go when we talk about activities.
In winter, they go skating in the park near their house.
We use gerunds after the expressions be busy, it’s no use, it’s no good, it’s (not) worth, what’s the use of …?, there’s no point in.
There’s no point in trying to fix this car.
We use gerunds after verbs such as avoid, admit, confess, deny, look forward to, mind, regret, risk, spend, suggest, etc.
He admitted stealing the money.
She regretted not telling the truth.
We spent the whole evening playing chess.
Infinitive or Gerund?
We can use the gerund (-ing form) OR the infinitive after the verbs start, begin, continue, like, love, prefer and hate.
He continued talking about the project.
He continued to talk about the project.
They love spending their free time in the open air.
They love to spend their free time in the open air.
We use the to–infinitive and NOT the gerund after the expressions would love / would like / would prefer.
I would love to travel round the world one day.
I would like to have more information on the subject.
We can use the bare infinitive (without «to») OR the gerund after the verbs see, hear, feel and watch. However, there’s a difference in meaning.
I saw them cross the street.
I saw the whole action.
I saw them crossing the street.
I only saw part of the action