This vs. These

This (determiner)

The (thing) here used in indicating something or someone nearby.

“This classroom is where I learned to read and write.”

This (determiner)

The known (thing) used in indicating something or someone just mentioned.

“They give the appearance of knowing what they’re doing. It’s this appearance that lets them get away with so much.”

This (determiner)

The known (thing) used in indicating something or someone about to be mentioned.

“When asked what he wanted for his birthday, he gave this reply: “[…]””

This (determiner)

A known (thing) used in first mentioning a person or thing that the speaker does not think is known to the audience. Compare with “a certain …”.

“I met this woman the other day who’s allergic to wheat. I didn’t even know that was possible!”

“There’s just this nervous mannerism that Bob has with his hands, and it drives me crazy.”

This (determiner)

which is current.

“It snowed this week.”

This (adverb)

To the degree or extent indicated.

“I need this much water.”

“Do we need this many recommendations?”

“We’ve already come this far, we can’t turn back now.”

This (pronoun)

The thing, item, etc. being indicated.

“This is the excellent foppery of the world, that, when we are sick in fortune,—often the surfeit of our own behaviour,—we make guilty of our disasters the sun, the moon, and the stars… — Shakespeare, King Lear, [http://en.wikisource.org/w/index.php?title=The_Tragedy_of_King_Lear&action=edit&section=4 Act 1. Scene 2.]”

This (noun)

Something being indicated that is here; one of these.

This (interjection)

Indicates the speaker’s strong approval or agreement with the previous material.

These (determiner)

plural of this

These (pronoun)

plural of this