they (pron.)

Old English he, pronoun of the third person (see paradigm of Old English third person pronoun below), from Proto-Germanic *hi- (source also of Old Saxon, Old Frisian, Middle Dutch he, hi, Dutch hy, Old High German he), from PIE *ki-, variant of root *ko-, the "this, here" (as opposed to "that, there") root, and thus the source of the third person pronouns in Old English. The feminine, hio, was replaced in early Middle English by forms from other stems (see she), while the h- wore off Old English neuter hit to make modern it. The Proto-Germanic root also is the source of the first element in German heute "today," literally "the day" (compare Old English heodæg).

The paradigm in Old English was: MASCULINE SINGULAR: he (nominative), hine (accusative), his (genitive), him (dative); FEMININE SINGULAR: heo, hio (nom.), hie, hi (acc.), hire (gen. and dat.); NEUTER SINGULAR: hit (nom. and acc.), his (gen.), him (dat.); PLURAL: (all genders) hie, hi (nom. and acc.), hira, heora (gen.), him, heom (dat.).

Pleonastic use with the noun ("Mistah Kurtz, he dead") is attested from late Old English. With animal words, meaning "male" (he-goat, etc.) from c. 1300.

Old English þæt, "that, so that, after that," neuter singular demonstrative pronoun ("A Man's a Man for a' that"), relative pronoun ("O thou that hearest prayer"), and demonstrative adjective ("Look at that caveman go!"), corresponding to masc. se, fem. seo. From Proto-Germanic *that, from PIE *tod-, extended form of demonstrative pronominal base *-to- (see -th (1)).

With the breakdown of the grammatical gender system, it came to be used in Middle English and Modern English for all genders. Germanic cognates include Old Saxon that, Old Frisian thet, Middle Dutch, Dutch dat "that," German der, die, das "the."

Generally more specific or emphatic than the, but in some cases they are interchangeable. From c. 1200 opposed to this as indicating something farther off. In adverbial use ("I'm that old"), in reference to something implied or previously said, c. 1200, an abbreviation of the notion of "to that extent," "to that degree." As a conjunction ("Not that I loved Caesar less, but that I loved Rome more") it originally was the neuter pronoun or adjective that used practically as a definite article qualifying the whole sentence.

Slang that way "in love" is attested by 1929. That-a-way "in that direction" is recorded from 1839. "Take that!" said while delivering a blow, is recorded from early 15c. That is, for "that is to say," is by late 12c. That's what "just so" is by 1790. The intensifier at that "as well, to boot" is by 1830, U.S. colloquial, perhaps from "(cheap) at that (price)," etc.