used as the subject or object of a verb to show what thing or things you are referring to, or to add information about the thing just mentioned. Whether to use that and which depends on whether the clause it introduces is restrictive or non-restrictive. A restrictive clause means that the information in the clause is necessary to understand the preceding noun. For a restrictive clause, use that. Let’s look at some sample sentences: To understand when to use that and when to use which, it’s important to keep in mind the difference between restrictive and nonrestrictive clauses. In formal American English, that is used in restrictive clauses, and which is used in nonrestrictive clauses. Not sure what that means? Let’s find out! Which can be an interrogative or a relative pronoun. Which can function as an interrogative pronoun. An interrogative pronoun (who, whom, whose, what, and which) is a pronoun used to ask direct or indirect questions. Examples: Which is the best book you read last year? “Which is the best restaurant in town?” Sam asked. Use which for things and who for people. Use that for things and, informally, for people. For example: The carpet which you bought has moth damage. (A carpet is a thing, so which is correct. NB: Using which without a comma is unpopular, especially in the US.) The carpet that you bought has moth damage. The meaning of WHICH is being what one or ones out of a group —used as an interrogative. How to use which in a sentence. Which as an interrogative determiner is used to ask about something in a set of things. For example: The blue bag is mine. → Which bag is yours? 'Which' specifies 'the blue bag' in a set of other bags. This one is the best. → Which one is the best? I want the blue bag. → Which bag do you want? Use 'which' or 'that' to introduce a restrictive clause, and 'which' to introduce a nonrestrictive clause. Before we begin, you should be warned that it’s time to put your grammar pants on, since we’re about to dive into the world of restrictive and nonrestrictive clauses. Meaning of which is whichin English. which is which. idiom. Add to word listAdd to word list. used in expressionsthat relateto being ableto seethe differencebetween two very similarthings or people. For the first few monthsthe babieslookedso alikeI couldn't tellwhich was which. SMART Vocabulary: related words and phrases. Knowing how to use which and that correctly is important because these words have different meanings and thus affect sentences’ meanings. If the details are crucial to the sentence, use that. If they aren’t crucial, use which. Which and that are probably words you use frequently.