Adjective clauses are subordinate clauses that function as adjectives. A clause must contain a verb (not a gerund or participle)! (that’s what makes it a clause).
•Examples of Adjective Clauses:
1. that we know
2. whom they visit on Christmas vacation
3. who came to the show
4. which gave us enough light
5. whose friends are not here
Notice: The words that, whom, who, which, whose often introduce adjective clauses. They are called relative pronouns.
You can join these adjective clauses, which are dependent remember, with an independent clause to form a complex sentence.
1. The neighbors that we know will be at our party.
2. Their grandparents, whom they visit on Christmas vacation, live in Denver.
3. The people who came to the show were delighted.
4. We hooked up several kerosene lanterns, which gave us enough light.
5. John, whose friends are not here, is depressed.
Notice: a quick word on punctuation… Sentence one does not set off the clause with commas, yet sentence two does. Why? It depends on the importance of the clause. In the first sentence, not all neighbors will be at the party – only neighbors that we know. This is important information needed in the sentence; therefore, you don’t set it off with commas. In the second sentence, the grandparents live in Denver whether you visit them at Christmas or not. The adjective clause is not important, but, rather, added information; therefore, commas are needed. Same goes for the other sentences: since only the people who came to the show were delighted, no commas are needed.
If you have several sentences in which one or more of the sentences merely describe elements in one of the other sentences, you can combine the sentences using an adjective clause.
•Examples:
Madrid is the capital of Spain. It is located on the Manzanares River. The Manzanares flows from north to south. (Ok, here are three sentences that are related. Look at the related elements: Madrid—it, Manzanares—flows. These sentences can be joined using adjective clauses.
Madrid, which is located on the Manzanares River which flows north and south, is the capital of Spain.
To make the sentence better, you can remove the which is.
I love my green sweater. I found it in the attic yesterday. (again, both sentences are talking about one thing—the sweater, so combine them using an adjective clause).
I love my green sweater that I found in the attic yesterday.
Or… I found the green sweater, that I love, in the attic yesterday. Depending on which is more important—the love of the sweater, or the finding of the sweater.
(See more examples in The Writing Guide "Using Clauses" Section)