This-That/ Indefinite articles

The words ‘this’ and ‘that’ are demonstrative pronoun which is used for indicating something. We use the word ‘this‘ to point out a person or object which is close to you. On the other hand, ‘that‘ is used to point out a person or an object which is farther from you.

BASIS FOR COMPARISON	THIS	THAT
Meaning	This is a pronoun and determiner used to identify someone or something near to the speaker.	That is a pronoun and determiner used to identify someone or something at a distance to the speaker.
Refers to	Something which is just mentioned.	Something which is previously mentioned.
Plural form	These	Those
Conjunction	No	Yes
Examples	Did you know this person?	That's not my cup of tea.
	The water of this river is clean and pure.	Bring me that book.
	This is a very simple exercise.	Who is that boy?

You can create questions:                                    You can use it in negative:

That is my computer.                                         That isn't/not my computer.

Is that my computer?                                        This isn't/not my dog.

Yes, that is.
No, that isn't.

This is my dog.

Is this your dog?

Yes, this is.

No, this isn't.

Indefinite article

A and AN are called indefinite articles. "Indefinite" means "not specific". Use A(AN) when you are talking about a thing in general, NOT a specific thing.

Examples:

• I need a phone. Not a specific phone, any phone
• Mark wants a bicycle. Not a particular bicycle, a bicycle in general
• Do you have a driver's license? In general

Use A(AN) when talking about a thing which is new, unknown, or introduced to a listener for the first time. Also use A(AN) when you are asking about the existence of something.

Examples:

• I have a car. The car is being introduced for the first time.
• Tom is a teacher. This is new information to the listener.
• Is there a dictionary in your backpack? Asking about the existence of the dictionary

Similarly, use A(AN) to introduce what type of thing we are talking about.

Examples:

• That is an excellent book. Describing the kind of book
• Do you live in a big house? Asking about the kind of house
• I ate a thick, juicy steak. Describing the kind of steak

REMEMBER: You cannot use A(AN) with plural nouns because A(AN) means "one" or "a single".

Examples:

• I saw a bears in Yellowstone National Park. Not Correct
• I saw bears in Yellowstone National Park. Correct