This article is not about the legal concept of a restrictive covenant.
Should one use "that" or "which"? In syntax, the concepts of restrictive clause and non-restrictive clause can perhaps most easily be explained by contrasting two examples:
- The Washington Monument, which is 555 feet tall, is the tallest building in Washington.
- The house that was recently built is Senator Smith's house.
Some writers follow a normative rule that "which" should be used in non-restrictive clauses and "that" should be used in restrictive clauses. In this usage, the phrase
- the house that is green
- the house, which is green.
Most writers do not adhere to this rule, perhaps considering it unnecessary to be explicit about the distinction.