Relative Clause Type #3: Preposition + Whom/Which
In many cases, a relative clause will need to start with a preposition. Prepositions are the small words that occur before places in space and time:
- at work
- after lunch
The second type of relative clause begins with a preposition before the relative pronoun whom or which:
- … to whom…
- … with which…

We have to solve this problem first. After we solve this problem, we can deal with the other issue.
We have to solve this problem first, after which we can deal with the other issue.
You can put the preposition before the relative pronoun or toward the end of the relative clause:
1. That’s the lady. You need to send the package to her.
- That’s the lady to whom you need to send the package.
- That’s the lady whom you need to send the package to.
2. That’s the equipment. We need to work with that equipment.
- That’s the equipment with which we need to work.
- That’s the equipment which we need to work with.
3. Thank you for your help. Without it, I couldn’t have finished this project.
- Thank you for your help, without which I couldn’t have finished this project.
- Thank you for your help, which I couldn’t have finished this project without.
4. I don’t remember the man. I got the message from him.
- I don’t remember the man from whom I got the message.
- I don’t remember the man whom I got the message from.
5. I can’t remember the supplier. We got that part from them last year.
- I can’t remember the supplier from which we got that part last year.
- I can’t remember the supplier which we got that part from last year.
Defining relative clauses starting with a preposition
If the information in the relative clause is needed to understand what the preceding noun/idea refers to, then we don't use a comma.
- Our greatest happiness does not depend on the condition of life in which chance has placed us, but is always the result of a good conscience, good health, occupation, and freedom in all just pursuits. (Thomas Jefferson)
- Accept the things to which fate binds you, and love the people with whom fate brings you together, but do so with all your heart. (Marcus Aurelius)
- Anger is an acid that can do more harm to the vessel in which it is stored than to anything on which it is poured. (Mark Twain)
- Shadow is the means by which bodies display their form. The forms of bodies could not be understood in detail but for shadow. (Leonardo da Vinci)
- Time is the fire in which we burn. (Gene Roddenberry)
where = in which/on which
That’s the village. I grew up in that village.
- That’s the village in which I grew up.
- That’s the village where I grew up.
That’s the farm. I grew up on that farm.
- That’s the farm on which I grew up.
- That’s the farm where I grew up.
thanks to whom
I'd like to thank John. Thanks to him, we were able to finish this project on time.
- I'd like to thank John, thanks to whom we were able to finish this project on time.
I’m grateful for the help provided by John’s department. Thanks to them, we were able to locate the records more quickly.
- I’m grateful for the help provided by John’s department, thanks to whom we were able to locate the records more quickly.
as a result of which
There’s been a big change in the market. As a result, we can longer do things the same way
- There’s been a big change in the market as a result of which we can longer do things the same way.
This is the problem. As a result of this problem, our project will be delayed.
- This is the problem, as a result of which our project will be delayed.