Participle clauses

A present participle clause can express:

• an action that happens at the same time as the action in the main clause:

  Tom lost his keys (while) walking through the park. (Tom lost his keys while he was walking through the park.)
  She left the room singing happily. (She left the room as she was singing happily.)

  The participle clause can come first in literary styles:

  (While) walking through the park, Tom lost his keys.

• an action that happens just before another action:

  Opening the envelope, I found two concert tickets. (I opened the envelope and I found two concert tickets.)

• an action that is the result of another action:

  Moments later a bomb exploded, leaving three people dead and twelve others injured.
  When I entered they all looked at me, making me feel uncomfortable.

• a reason for the action in the main clause:

  Having nothing left to do, Paula went home. (Since Paula had nothing left to do, she went home.)
  Knowing a little Russian, I had no difficulty making myself understood. (As I knew a little Russian, I had no difficulty making myself understood.)
  Working as a sales rep, I get to travel a lot. (I travel a lot because I work as a sales rep.)

  Here the subjects of the two actions can be different:

  The weather being nice, we decided to go for a picnic. (As the weather was nice, we decided to go for a picnic.)

Perfect participle clauses

If we want to make it clear that an action happens before another one, we use a perfect participle for the earlier action:

Having washed the car, I noticed a small scratch on the front right fender. (After I washed the car, I noticed a small scratch on the front right fender.)

Here the present participle (washing the car) would mean "while I was washing the car".

If the two actions do not follow each other immediately or if the first action happens over a period of time, we use a perfect participle instead of a present participle for the earlier action:

Having seen the film before, I didn't want to go to the cinema.
Mark knew the town well, having lived there all his life.

Past participle clauses

Past participle clauses replace passive voice finite clauses:

Shocked by the explosion, the people ran for shelter. (The people were shocked by the explosion and ran for shelter.)
The musicians stood up, surrounded by thunderous applause. (The musicians stood up while they were surrounded by thunderous applause.)

If we want to emphasise that an action happens before another one, we use a passive perfect participle:

Having been nominated three times for an Oscar, he is one of today's most acclaimed film directors.

Participle clauses replacing a relative clause

A present participle clause can replace an active voice finite relative clause. The noun before the participle is the doer of the action:

The man driving the car was not injured. (The man who was driving the car was not injured.)

Present participle clauses are possible even with verbs which are not normally used in the continuous form (state verbs):

If you think you have received an e-mail containing a virus, you should delete it immediately. (If you think you have received an e-mail which contains a virus, delete it immediately.)

A past participle clause can replace a passive voice finite relative clause. The noun before the participle is its object:

This is the last photograph taken of my grandmother. (This is the last photograph that was taken of my grandmother.)

See also: http://www.grammaring.com/hardly-scarcely-barely-no-sooner 

Relative clauses

 A relative clause is one kind of dependent clause. It has a subject and verb, but can’t stand alone as a sentence. It is sometimes called an “adjective clause” because it functions like an adjective—it gives more information about a noun.
A relative clause always begins with a “relative pronoun,” which substitutes for a noun, a noun phrase, or a pronoun when sentences are combined.

The relative pronouns are:

who	for people	can substitute for subject nouns/pronouns (he, she, we, they)
whom	for people	can substitute for object nouns/pronouns (him, her, us, them)
whose	for people	can substitute for possessive nouns/pronouns (his, hers, our, their)
that	for people or things	can be either subject or object can only be used in restrictive relative clauses (see below)
which	for things	can be either subject or object can be used in non-restrictive relative clauses can also be used in restrictive relative clauses, though some people don’t like this use

Relative pronoun as subject (in red):

I like the person. The person was nice to me.

I like the person who was nice to me.

I hate the dog. The dog bit me.

I hate the dog that bit me.

I am moving to Louisville, KY. It is home to the Muhammad Ali Museum.

I am moving to Louisville, KY, which is home to the Muhammad Ali Museum.

Relative pronoun as object (in red):

I like the bike. My father gave me the bike.

I like the bike that my father gave me.

Restrictive Relative Clauses

Restrictive relative clauses give information that defines the noun—information that’s necessary for complete identification of the noun. Use “that” or “which” for non-human nouns; use “that” or “who” for human nouns. Do not use commas.

I like the paintings. (Which paintings? We can’t clearly identify them without the relative clause.)

So we add the clause:

The paintings hang in the SASB North lobby.

I like the paintings that hang in the SASB North lobby.

OR

I like the paintings which hang in the SASB North lobby. (Again, this is acceptable, but some people object to using “which” in a restrictive relative clause. “That” is preferred.)

Students who study hard will do well in my class. (Only this group of students will do well.)

Students whose grades are low can drop one test score. (Only this group can drop a test score.)

When the noun is the object of the preposition, both the noun and the preposition move together to the front of the relative clause. In less formal English, it’s common to move only the pronoun to the front of the clause.

I spent hours talking with a person last night. I hope to hear from her.

I hope I hear from the person with whom I spent hours talking last night. (more formal)

OR

I hope to hear from the person whom I spent hours talking with last night. (less formal)

Non-restrictive Relative Clauses

This type of relative clause merely provides extra information. The information may be quite interesting and important to the larger conversation, but it is not essential for precise identification of the noun. “That” cannot be used as a relative pronoun in a non-restrictive relative clause. Commas are always used at the beginning and end of this type of relative clause.

A non-restrictive relative clause can modify a single noun, a noun phrase, or an entire proposition.

My mother is thinking of opening a restaurant. My mother is an excellent cook.

“My mother” is already a clearly defined noun, so the second sentence becomes a non-restrictive relative clause set off by commas on both sides.

My mother, who is an excellent cook, is thinking of opening a restaurant.

I’m planning to grow roses. I find roses quite beautiful.

I’m planning to grow roses, which I find quite beautiful.

(not okay) I’m planning to grow roses, that I find quite beautiful.

I’m driving across the country with three small children.

Driving across the country with three small children is going to be stressful.

I’m driving across the country with three small children, which is going to be stressful.

Reducing Relative Clauses

Some types of relative clauses can be “reduced”— the relative pronoun and maybe other words can be removed. You might reduce the clause to make your writing more concise or to add sentence variety. We’ll use the examples above to demonstrate how to reduce both restrictive and non-restrictive clauses.

Restrictive relative clauses can be reduced in two ways.

Subject pronouns can be deleted if –ing is added to the verb.

I like the paintings that hang in the SASB North lobby.

I like the paintings hanging in the SASB North lobby.

Object pronouns can be deleted.

I like the bike that my father gave me.

I like the bike my father gave me.

Non-restrictive relative clauses can be reduced in one way.

Subject pronouns with “be” verbs can be deleted in non-restrictive clauses.

I am moving to Louisville, KY, which is home to the Muhammad Ali Museum.

I am moving to Louisville, KY, home to the Muhammad Ali Museum.

My mother, who is an excellent cook, is thinking of opening a restaurant.

My mother, an excellent cook, is thinking of opening a restaurant.

Subject-Verb Agreement in Relative Clauses

Remember that the relative pronoun is substituting for a noun, which could be singular or plural before the substitution. The verb in the relative clause must agree with the original noun.

People are lucky. People win the lottery.

People who win the lottery are lucky. (plural verb)

A person is lucky. She wins the lottery every year.

A person who wins the lottery every year is lucky. (singular verb)

Agreement can be tricky in “one of the…” constructions. The key is to find which noun the relative pronoun is referring to.

Homelessness is a problem. The problem needs to be addressed.

Homelessness is a problem that needs to be addressed. (singular problem)

Many problems need to be addressed. Homelessness is one of the problems.

Homelessness is one of the problems that need to be addressed. (plural problems)

Source: https://writingcenter.unc.edu/relative-clauses/

Other references: https://dictionary.cambridge.org/grammar/british-grammar/relative-clauses/relative-clauses-defining-and-non-defining

https://learnenglish.britishcouncil.org/es/category/grammar/grammar-relative-clauses-who-which-that-whose