A relative clause is a subordinate clause that functions like an adjective to modify nouns or pronouns. It provides additional information about the antecedent, which is the word being modified. For example, in the sentence 'The student who studies hard will succeed', 'who studies hard' is the relative clause that modifies 'the student'.
Relative pronouns are words that introduce relative clauses and connect them to the main clause. The most common relative pronouns are who, whom, whose, which, and that. 'Who' is used for people as subject or object. 'Whom' is used for people as object only. 'Whose' shows possession. 'Which' is used for things. 'That' can be used for both people and things in restrictive clauses.
There are two main types of relative clauses. Restrictive or defining clauses provide essential information that identifies the noun. They don't use commas and can use 'that'. For example, 'The book that I borrowed is interesting' - we need to know which book. Non-restrictive or non-defining clauses add extra information about a noun that's already identified. They use commas and cannot use 'that'. For example, 'My car, which is red, needs repair' - we already know which car.
Relative adverbs are another way to introduce relative clauses. 'When' refers to time, as in 'I remember the day when we met.' 'Where' refers to place, like 'This is the school where I studied.' 'Why' refers to reason, such as 'Tell me the reason why you left.' These adverbs often replace preposition plus which combinations, making sentences more natural and concise.
Let's practice with some examples. 'The girl who sits next to me is very smart' - this is restrictive because we need to know which girl. 'London, where I was born, is a big city' - this is non-restrictive with commas because we already know which city. 'The book that you recommended is excellent' - restrictive again, identifying which book. Remember to identify the antecedent, choose the correct relative word, and use commas appropriately. With practice, you'll master relative clauses!