English has three relative adverbs — where, when, and why. They work like relative pronouns, but instead of replacing a noun they replace the combination of a preposition and which. The result is shorter and more natural in most contexts.
Each one links a noun to a clause that describes it — a place, a time, or a reason.
Where
Where introduces a clause about a place. It replaces in which, at which, or another locative preposition + which.
In formal writing you may see in which or at which instead. In everyday English, where is the standard choice.
Where in non-defining clauses
When the place is already identified — a proper noun or a unique reference — the clause adds extra information and takes commas.
The comma signals that the clause could be removed without changing which place is meant.
When
When introduces a clause about a time. It replaces in which, on which, at which, or during which — whichever preposition fits the time expression.
Like where, it appears in both defining and non-defining clauses.
Dropping when
In defining clauses, when can often be dropped with no change in meaning.
Both versions — with and without when — are correct. Dropping it is common in speech and informal writing.
Why
Why introduces a clause about a reason. It replaces for which and almost always follows the noun reason.
Dropping why
Why is dropped more often than it is kept. All three forms below are correct, and each is common:
The version without any linking word is the most frequent in spoken English.
Relative adverb vs. preposition + which
Every relative adverb has a formal equivalent built from a preposition and which. The choice is a matter of register, not meaning.
| RELATIVE ADVERB | FORMAL EQUIVALENT |
|---|---|
| where | in / at / on which |
| when | in / on / at / during which |
| why | for which |
A few points to keep in mind:
- The preposition + which form sounds more formal and is typical of academic or legal writing.
- The relative adverb form is shorter and fits most everyday contexts.
- A third option exists for when and why: drop the relative word entirely. This works in defining clauses but not in non-defining ones.
All three are grammatically correct. Choose the one that fits the tone of your sentence.
When you cannot drop the relative adverb
Not every relative adverb is optional. Two patterns require it to stay.
Non-defining clauses. The relative adverb (or pronoun) cannot be removed when commas are present.
Where in defining clauses. Unlike when and why, where is rarely dropped in defining clauses. The sentence usually becomes awkward or unclear without it.
If you want to remove where, restructure with a preposition at the end: The café we met at is still open.
Common mistakes
Using which instead of where for places
Adding a pronoun after where
Adding a preposition after where
Dropping where when it is needed
Using when/why in non-defining clauses without commas