that

that

is a word with many roles, and plays a major part in English sentence structure. The following are its main grammatical functions:

demonstrative pronoun:

That was what I meant

demonstrative adjective:

Why did you take that picture of me?

demonstrative adverb:

I was that angry / It didn't hurt that much

relative pronoun:

It was not the drug that had done it

conjunction:

He had assumed that we would want to see him

1. As a demonstrative pronoun and adjective, that normally refers to something already mentioned or known: (pronoun) She had not meant it so, but it could have been read like that / How the hell did you manage that? / The witnesses, if they could be called that, continued to repeat that they knew nothing / (adjective) If I were you, I would keep an eye on that young man / It wasn't a nature reserve, that Ark of yours. There are also a number of familiar idiomatic or formulaic uses: Something worth a lot of money, that's for sure / She had a small, pretty face, I'll give you that / She cleared her throat to speak but left it at that / I just wanted to see her, that's all.

2. Its use as a demonstrative adverb equivalent to so or very (or so very) dates from the 15c and has been slipping in and out of standard usage ever since. In current English it tends to be informal, more so perhaps in positive contexts (typically in questions and conditions) than in negative contexts:

• ‘Shut up,’ says Claudia…‘It's not that funny’ —David Lodge, 1988

• You and your brother, you're not really that alike, are you? —Encounter, 1989

• I promise that if I'm that tired, I will pull over and take a break —weblog, BrE 2003 [OEC]

• Was he really that angry with me? —fiction website, BrE 2004 [OEC].

3. As a relative pronoun, that becomes an alternative to which (and occasionally who). Although they are often interchangeable, there are some uses that are peculiar to each:

a) When that is used it normally introduces a so-called ‘restrictive’ clause, which defines or gives essential (rather than additional) information about the noun or noun phrase that comes before: the pen that my father bought for me / the pen that is over on the table / (in each case the that-clause defines which pen is meant). (See further at relative clauses). In these cases the that-clause normally follows on without a comma. Which can also be used in these examples, but in conversational English that is more usual, and in some cases it is possible to omit the relative pronoun altogether and say the pen my father bought for me. That can also replace who (or whom), especially when the reference is non-specific, as in The person that I saw was definitely a woman, and when there are two antecedents, one inanimate and the other human: It was the drug and not her brother that had upset her.

b) That is also more idiomatic than which in a number of cases: (1) when which already occurs earlier in the sentence in another role (Which is the house that you bought?), (2) after indefinite pronouns such as anything, everything, nothing, and something (There is something that I forgot to mention), and (3) after a construction with the impersonal it (It is the new one that we want). When that is the object of the verb in its clause, it is regularly omitted, especially in speech (There is something I forgot to mention).

c) Which, not that, has to be used in so-called non-restrictive clauses which give additional rather than essential information: A new edition of the book, which has taken ten years to write, will be published this week. Which is also used when a preposition precedes it (Is this the book to which you are referring?); in a corresponding construction with that, the preposition has to come at the end (Is this the book that you are referring to? or Is this the book you are referring to?).

4. That is used as a conjunction to introduce a subordinate clause, principally after verbs of saying, feeling, believing, knowing, learning, etc.: The President admitted that he had lied / We would hate to think that they were corrupting you / I understand that you wanted to see me. A that-clause of this type can also occur after the impersonal it: It was natural that they should think so. Normally the conjunction that can be omitted, especially in speech: I understand you wanted to see me / It was natural they should think so. In inverted constructions, however, in which the that-clause comes before the main clause, that is obligatory: That they are guilty is assumed by everybody.