The word that is widely used in English for a variety of functions.  We'll look briefly at eight uses of that in this section of the lecture.  Because it's used so many ways, the word can be a challenge for us as teachers when we are using authentic materials.  We can trip up if we're not careful--and have the embarrassing task of going back to class with new information after we've mishandled a question from a student.  (One of the characteristics of more experienced teachers is that we have learned that we are going to make mistakes, that our mistakes are generally not fatal to our students, and that we learn from those mistakes as painful as the learning seems in the moment.)

That is paired with this (and these and those) to combine with nouns: this book, that book, this music, that music, these books, those books.

This function is variously labeled in grammar books: demonstrative, demonstrative adjective, and determiner. Students have to learn to combine this/that with singular and noncount nouns and these/those with plural nouns.  The more difficult task for us is to help students learn the meaning of these forms.  Generally, this/these are used to point out items or topics "close" to the speaker/writer while that/those are somehow "distant" from the speaker/writer.

This use as a determiner has a related use as a freestanding pronoun.

That can be used as a freestanding pronoun (rather than a determiner) in phrases such as these quoted from the Longman Grammar of Spoken and Written English:
 

The Longman Grammar shows that on the whole in English the demonstrative pronouns are rare compared to the personal pronouns.  Additionally, demonstratives are more common in conversation than in writing. 

Also they show that that is much more common than the other 3 demonstrative pronouns! Somehow we find that more useful than the other demonstratives -- perhaps because of using set phrases like that's as in the example sentences. 

It's this kind of information that corpus linguistics can provide that is just wonderfully useful for language teachers.  The traditional approach shows that English has a system with 4 words in it--and those words paired into sets based on number (on singular vs. plural nouns).  But, in actual use, the system doesn't quite work as in the traditional presentation.  Yes, the little closed system does involve four words; yes, the system involves meanings that contrast this/these with that/those; but the four words in the system are not used in equal amounts and are not of equal value to our ESL/EFL students.

That can be used to intensify the meaning of an adjective--it's that hot, he's that tired, I'm that old, and so forth. These uses are found primarily in conversation.

That is also used as a relative pronoun: I bought the book that is required for this course.  The Longman Grammar found that that as a relative pronoun is more common in academic writing and newspaper writing than in conversation.  Indeed, conversation tends to have more of those sentences where the relative pronoun is dropped: I bought the book required for this course. 

Look at the sentences in the box.  In each, the verb is followed by that plus a clause.  The that + clause combination is called a noun clause because it functions like a noun as the direct object of the verb.  Grammar books also discuss the structure as a "verb complement"--because the that + clause "completes" the meaning and structure of the verb.  This use is very common in academic writing--notice the verbs that are used: claim that, figured that, find that, conclude that, know that, suspect that.  These and other verbs like them are used to report knowledge--a very common function in academic writing.  However, we use these clauses often in conversation, too, with verbs like think, know, and others that show our own ideas and knowledge.  In conversation, there's a tendency to drop the that, however, so these noun clauses are often in the form: I think he's a really nice guy.
 

Appositive clauses look a lot like relative clauses, but they are fundamentally different in structure.  Remember that a relative clause is a changed sentence: a relative pronoun is subsituted for some noun phrase in the source sentence and thus the relative pronoun has a dual role--to connect the clause to a noun but also to be a structural part of the clause itself.  Look at this example: that is the subject of the relative clause:  How do I know that?  Well, figure out the sentence that is the source for the relative clause. 

This is the sentence that is changed to make the relative clause: The book is required for this course.  To make the relative clause, that is put into the subject position: that is required for this course.

So, that in a relative clause is not just a connecting word; it must be subject or object.  And that (like all relative pronouns) must have some meaning that is understandable in its sentence.  In our example, that = the book.

An appositive is a phrase that names (or labels) a noun as in these examples with the appositive in bold type.  Appositives are "postmodifiers" of nouns; they mean the same thing as the noun they are attached to.  Sometimes an appositive is given without commas, sometimes with commas. 
 

An appositive clause is a subordinate clause that has the same kind of function with a noun as other types of appositives.  It names or labels or specifies the noun.

In contrast to a relative clause, an appositive clause involves a simple connection: that connects a clause without being a part of the subordinate clause.

What sentences are combined? 

That combines the two, but it isn't a part of the second clause.  These appositive clauses are related to similar noun clauses:  I believe that English grammar is fascinating = my belief that English grammar is fascinating.... The process of changing verbs into nouns is called nominalization.

Appositive clauses involve nouns like belief, thought, knowledge, conclusion; these words are the noun forms of related verbs believe, think, know, conclude that often take noun clauses as their objects.

Here are some examples from the sociology textbook that I'm using for examples for this course.  Try analyzing these examples.  Can you tell that they are not relative clauses? 
 
 

But be careful to analyze the sentences that you find rather than assuming that a word like idea will always involve an appositive clause.  Compare these two sentences--which is the relative clause?  which the appositive clause?
 

Let's try one more: is the clause in this sentence a relative clause or an appositive clause?
 

That is found in phrases such as that is, which is used primarily in academic writing.  Even in that context, that is is must less common than other phrases such as so however, thus, and therefore. 

Comparisions can be structured using so + adjective + that :  He was so tired that he couldn't do his sociology homework.  She was so hungry that she ate a snack before dinner. 

Adverbial subordinators: given that, granted that, provided that, seeing that, supposing that, now that, in that....

For example: Given that the portfolio is a graduation requirement, you cannot graduate until you have completed yours and it has been approved by your adviser.

Let's see: 

1. That is a very common word.

2. The demonstrative pronoun that is more common in conversation than in writing. 

3. While all four of the demonstratives exist as a system, that is used a lot more than the other three. 

4. The relative pronoun that is more common in academic writing than in conversation.  Academic writing involves use of long, complicated noun phrases to be as specific as possible about a topic.  Conversation is more generalized and dependent on context to make meanings clear. 

5. Also that tends to be dropped in conversation.

Please email me your questions and comments. Thanks.

Biber, D., Johansson, S, Leech, G., Conrad, S., and Finegan, E.  (1999).  Longman grammar of spoken and written English.  Harlow, England: Pearson Education Limited.