THE -ING FORMS

The -ing forms.

A verb ending in -ing is either a present participle or a gerund. These two forms look identical. The difference is in their functions in a sentence.

Uses

The -ing form of a verb has both noun uses and adjectival (or adverbial) uses. In either case it may function as a non-finite verb (for example, by taking direct objects), or as a pure noun or adjective. When it behaves as a non-finite verb, it is called a gerund in the noun case, and a present participle in the adjectival or adverbial case. Uses as pure noun or adjective may be called deverbal uses.
The distinctions between these uses are explained in the following sections.

Formation

All English verbs (except for modals and other defective verbs which do not have gerunds or participles) make the inflected form in -ing regularly. Thus go makes going, read makes reading, fail makes failing, and so on. In certain cases there are spelling changes, such as doubling of consonants (as in sit → sitting) or omission of mute e (as in change → changing). For details of these rules, see English verbs.

1. Present participles

A present participle is most commonly used as part of the continuous form of a verb, after verbs of perception, after verbs of movement, or as an adjective.

1.1 Present participles as part of the continuous form of a verb

Present participles are an element in all continuous verb forms (past, present, future, conditional, etc.). The helping verb will indicate the tense, while the present participle remains unchanging.

Examples

• He is painting.
• She was waiting.
• They will be coming.
• We would be staying.
• I would have been leaving.

1.2. Present participles after verbs of perception

Present participles can be used after verbs of perception in the pattern verb + object + present participle to indicate the action being perceived.

Examples

• We saw him swimming across the pond.
• I watched her painting Sarah's portrait.
• I couldn't hear her singing because of the noise.
• I would like to see you knitting sometime.

1.3. Present participles after verbs of movement, action, or position, to indicate parallel activity.

Examples

• She sat looking at the sea.
• He walks reading his newspaper.
• I cook listening to the radio.
• Sally lay listening to the bugs in the grass.

1.4. Present participles as adjectives

Examples

• Did you read that amazing book?
• This movie is so exciting!
• His economics class is boring.

1.5.  Special expressions + verb-inghave: fun, a good time, a hard time, trouble, difficulty, etc.
She had a good time watching the ice skating competition.
I'm having such a hard time getting motivated * I had a hard time getting over the

social and language barriers. (se me ha hecho difícil superar)

spend time, waste time
He spends a lot of time playing computer games.
sit, stand, or lie + expression of place
I stood at the bus stop waiting for 45 minutes.
  
find or catch + (pro)noun I found the cat sleeping in my bed.
Read more about using present participles.

2. Gerunds

The gerund always has the same function as a noun, although it looks like a verb. It can be used in the same way as a noun.

2.1. A gerund as the subject of the sentence

Examples

• Eating people is wrong.
• Driving too fast is dangerous.
• Walking is good for you.
• Your knitting it beautiful.

2.2 A gerund after prepositions

Examples

• Can you sneeze without opening your mouth?
• She is good at painting.
• I was the fastest at climbing the rope.
• He learns music by listening to the chords.

2.3. A gerund after certain specific verbs

Examples

• I like cooking.
• He enjoys walking.
• They hate milking cows.
• I can imagine drifting away in a balloon.

2.4. A gerund in compound nouns

Examples

• I took her to her driving lessons.
• We are going to the swimming pool.
• My uncle does a lot of bird-watching.
• I found this pie by dumpster-diving.