These constantly used words function as both pronouns and adjectives. Brief comments about them are as follows: (1) The plural of this is these; the plural of that is those: "This man," "these men," "that woman," "those women." (2) This and that can be used to mean "how much" and "how many": "I know this much." "I know that much." "I saw that many." "I knew this many." (3) This, that, and their plural forms (these, those) are demonstrative pronouns, which means that they refer to something that can be pointed out: "This is my hat." "That is yours." "These are my gloves." "Those are your books." "Is this you?" "Is that you in the dark?" (4) This and its plural can represent or sum up words that follow: "Let me tell you this."The steps you should take are these...." (5) This should be used to indicate a person, idea, event, or statement which is considered present, near, just mentioned, or supposed to be understood: "This situation now confronting us...." "This idea you have expressed...." "Give us this day our daily bread." That should be used to indicate a person, idea, event, or statement which has not been mentioned before or is not immediately present: "That is a lovely sight." "Where were you that day?"
Dictionary of problem words and expressions. Harry Shaw. 1975.