The placement of prepositions in relative clauses depends on its formality. Prepositions often go to the end of the relative clauses when it’s informal, and show up before the relative pronouns when it’s formal.
Example
- The book (that) I borrowed from the library is due tomorrow. (Informal)
- The company with which we partnered is expanding to new markets. (formal)
Here are some commonly used prepositions with relative pronouns and examples in both formal and informal styles:
- At: The cafe at which we met (formal) / The cafe we met at (informal)
- By: The method by which they solved the problem (formal) / The method they solved the problem by (informal)
- For: The reason for which she was late (formal) / The reason she was late for (informal)
- In: The town in which I grew up (formal) / The town I grew up in (informal)
- Of: The friend of whom I spoke (formal) / The friend I spoke of (informal)
- On: The day on which it happened (formal) / The day it happened on (informal)
- To: The person to whom I gave the gift (formal) / The person I gave the gift to (informal)
- With: The colleague with whom I work (formal) / The colleague I work with (informal)
References