The Use Of Where, Why And When - Relative Clauses and Preposition Use.

Where, referring to a place, why, referring to a reason, and when, referring to a time, can be used instead of a relative pronoun after a noun.

In defining relative clauses why and when, unlike where can be omitted.

Example: I'd like to know the reason (why) he decided not to come.February is the month (when) many of my colleagues take skiing holidays.
BUT! She always had wanted to go to a place where she could speak her native tongue.
When, where and why are not omitted in non-defining relative clauses.

Example: I come from the Seattle area, where many successful companies such as Microsoft and Boeing are located, and I often go home during the summer.He likes shopping between one and three, when most people are at home, because of the relative calm.

NOTES:
When speaking, we often omit the relative pronoun.
Whom is formal and most often used when writing.