…the time at which the original mineral was formed.
After place, room, street, and words such as year and month, you can use in which instead of where or when.
…the place in which they found themselves.
…the room in which the meeting would be held.
…the year in which Lloyd George lost power.
After day you can use on which instead of when.
Sunday was the day on which we were expected to spend some time with my father.
After reason you can use that or no pronoun instead of why.
…the reason that non-violence is considered to be a virtue.
That’s the reason I’m checking it now.
After words such as situation, stage, arrangement, or system you can use in which instead of where or whereby.
…a situation in which there’s a real political vacuum.
Additional points about non-defining relative clauses
8.109 In written English, you can use a non-defining clause, that is, a clause that simply gives extra information, to say that one event happened after another.
For example, instead of saying I gave the book to George. George then gave it to Mary, you can say I gave the book to George, who gave it to Mary.
I sold my car to a garage, who sold it to a customer at twice the price.
The hot water ran on to the ice, which promptly melted.
Later he went to New Zealand, where he became a teacher.
commenting on a fact
8.110 You can use a non-defining clause beginning with which to say something about the whole situation described in a main clause, rather than about someone or something mentioned in it.
These computers need only tiny amounts of power, which means that they will run on small batteries.
I never met Brando again, which was a pity.
Before the exam she was a little tense, which was understandable.
commenting on a time or situation
8.111 When you want to add something to what you have said, you sometimes use a non-defining clause beginning with a preposition, which, and a noun, to add extra information. The noun is often a word like time or point, or a very general word for a situation like case or event.
They remain in the pouch for some seven weeks, by which time they are about 10 cm long.
I was told my work was not good enough, at which point I decided to get another job.
Sometimes you may feel too weak to cope with things, in which case do them as soon as it is convenient.
Nominal relative clauses: What you need is …
8.112 When it is difficult to refer to something by using a noun phrase, you can sometimes use a special type of relative clause called a nominal relative clause.
What he really needs is a nice cup of tea. Whatever she does will affect the whole family.
8.113 Nominal relative clauses that begin with what can be used. What can mean either the thing that or the things that.
What he said was perfectly true.
They did not like what he wrote.
I believe that is a very good account of what happened.
I’m what’s generally called a dustman.
People often use a what-clause in front of is or was to say what kind of thing they are about to mention.
What I need is a lawyer.
What you have to do is to choose five companies to invest in.
These structures are explained in paragraphs 9.28 to 9.30.
For another use of what in nominal relative clauses see paragraph 8.116.
8.114 Nominal relative clauses that begin with where are usually used after a preposition or after the verb be. Where means the place where.
I crossed the room to where she was sitting.
He lives two streets down from where Mr Sutton works.
This is where I crashed the car.
8.115 Nominal relative clauses beginning with whatever, whoever, or whichever are used to refer to something or someone that is unknown or indefinite.
Whatever is used only to refer to things. Whoever is used to refer to people. Whichever is used to refer to either things or people.
Whatever, whoever, and whichever can be used as pronouns. Whichever is often followed by of.
I’ll do whatever you want.
I want to do whatever I can to help them.
You’ll need written permission from whoever is in charge.
People will choose whichever of these systems they find suits them best.
Whatever and whichever can also be used as determiners.
She had had to rely on whatever books were lying around there.
Choose whichever one of the three methods you fancy.
For more information about whatever, whoever, and whichever see paragraph 8.42.
8.116 What can be used with the same meaning as whatever, both as a pronoun and a determiner.
Do what you like.
We give what help we can.
The main use of what in nominal relative clauses is explained in paragraph 8.113.
Nominal that-clauses
8.117 A nominal that-clause is a type of subordinate clause that functions like a noun, and is introduced by that. When this type of clause is used to say what someone says or thinks (e.g. She said (that) she was leaving), this grammar refers to it as a reported clause.