This is used to reference a person or a thing.(pronoun)
An example of this is someone talking about and pointing at a plant which they are holding.
This means so.(adverb)
An example of this used as an adverb is the phrase "this big" being spoken as someone holds their hands a foot apart implying how big of a box they need.
See this in Webster's New World College Dictionary
pronoun pl. these
Origin: ME this, thes < OE thes, masc., this, neut. < base of the demonstrative pron.: see that
adjective pl. these
See this in American Heritage Dictionary 4
pron. pl. these these (Þēz)
Origin: Middle English
Origin: , from Old English; see to- in Indo-European roots. Usage Note: This and that are both used as demonstrative pronouns to refer to a thought expressed earlier: The letter was unopened; that (or this) in itself casts doubt on the inspector's theory. That is sometimes viewed as the better choice in referring to what has gone before (as in the preceding example). When the referent is yet to be mentioned, only this is used: This (not that) is what bothers me: we have no time to consider late applications. • This is often used in speech and informal writing as an emphatic substitute for the indefinite article to refer to a specific thing or person: You should talk to this friend of mine at the Department of Motor Vehicles. I have this terrible feeling that I forgot to turn off the gas. It is best to avoid this substitution in formal writing except when a conversational tone is desired. See Usage Note at that.
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