"I met a man. He works at your company." Two sentences, both correct, both slightly childlike. Joined: "I met a man who works at your company."

Which word to use

  • who — people: "the colleague who called you"
  • which — things: "the report which arrived late"
  • that — people or things, in defining clauses: "the report that arrived late"
  • where — places: "the office where I used to work"
  • whose — possession: "the client whose contract expires in June"

The comma question

This is the part that trips people up, and it changes meaning.

Defining — no commas

The clause identifies which one you mean. Remove it and the sentence loses essential information.

"The employees who work weekends get extra pay." (only those employees)

Non-defining — commas

The clause adds extra information about something already identified.

"The employees, who work weekends, get extra pay." (all of them work weekends, and all get extra pay)

Two commas change the meaning entirely. In contracts and policies, this distinction has consequences.

Two rules for non-defining clauses

  • Never use that — "My manager, that joined last year" is wrong. Use who.
  • Always use both commas, not just one

When you can drop the word entirely

If the relative word is the object of the clause, you can leave it out in speech:

  • "The book (that) I read last week."
  • "The person (who) you met yesterday."

But not when it is the subject: "The man who called" cannot lose its who.