Quenya has a definite article i that is more or less equivalent to English “the”: i atan = “the man” [human]. Like English, the definite article is used to specify a definite thing specifically referred to (“the man”), as opposed to an indefinite thing (“a man”). Unlike English, there is no indefinite article in Quenya (English “a”); indefinite nouns are simply unmarked: atan = “(a) man”.
Like English, Quenya may use i in the titles of persons, especially for divinity: i Ataren ar i Yondon ar i Airefëan “The Father, the Son and the Holy Spirit” (VT43/36); i Héru aselyë “the Lord is with thee” (VT43/28), i Eru “the One” (UT/305). However, Quenya seems less inclined to use the definite article for sobriquets: Atanatar Alcarin vs. “Atanatar the Glorious” (LotR/1038), Varda Aratarya (lit. “Varda [in] her sublimity”) vs. “Varda the Sublime”; Quennar Onótimo vs. “Quennar the *Reckoner” (MR/50), though the last of these did also appear as Quennar i Onótimo (MR/48). The definite article is, however, used in the title of documents and narratives: i Equessi Rúmilo “The Saying of Rúmil” (WJ/398); i Túrin i Cormaron “The Lord of the Rings” (PBL).
In cases where two definite nouns were part of a single phrase, Quenya often only marks the first of these with a definite article: i Valaron arcanwar “the thrones of the Valar [lit. the Valar’s thrones]” (PE22/147); i arani Eldaron “the kings of the Eldar” (WJ/369); i tyulma ciryava “the mast of the ship” (PE21/80); i coimas Eldaron “the lembas of the Eldar” (PM/395). The last of these also appears as i·coimas in·Eldaron (PM/403); see below for a discussion of in. The phrase i tyulma ciryava also appeared as tyulma i ciryo (“mast of the ship”), perhaps emphasizing the definiteness of this ship over the definiteness of the mast.
In all the examples in the previous paragraph, one of the nouns in the phrase is inflected in the genitive or possessive-adjectival cases. This may be a factor in this construction. English has no problem saying “the ship’s mast” vs. “the mast of the ship” with only one noun marked with definite article. The phrase i tulma ciryava may simply be a parallel of that construction, but with Quenya’s extra freedom in arranging inflected nouns. In one place Tolkien said that the definite article could be omitted completely in such cases:
note article = “the” is usually not used when noun is defined by a possessive or genitive [referring to elen síla lúmenn’ omentielvo “a star shines on the hour of our meeting”, as opposed to *i lúmenn’ omentielvo] (PE17/13).
There are a few other examples where Quenya seems to omit the definite article where it would be required in English, notably Anar “the Sun” and Isil “the Moon”. However, a more likely interpretation is that these are actually proper names, more equivalent to English “Sol” and “Luna”, and an Elf would not say i Anar any more that an English speaker would say “the Jupiter”.
The presence or absence of the definite article influences the meaning of plural forms, much as it does in English:
Definite were plurals referring to whole classes, to things naturally or habitually considered in plurality (as English heavens = “the sky”, the sands = “all the sand in a given locality”, etc.), and in the syntax of many languages a plural with a definite article, meaning all the members of a group previously mentioned, or in mind. Thus in Q. Eldar (not with article!) = “Elves, the Elves, All Elves”; i Eldar = “(all) the Elves previously named” (and in some cases distinguished from other creatures); but Eldali, “Elves, some Elves”. With Eldali the definite article is seldom used (VT49/8).
Thus much like English, Eldar mante coimas = “Elves ate lembas (as a general rule)” vs. i Eldar mante coimas = “the Elves ate lembas (referring to this specific group)”. For further discussion see plural nouns.
Conceptual Development: Tolkien introduced the definite article i very early. It is mentioned in both the manuscript and typescript versions of the Early Qenya Grammar from the 1920s:
Definite article. i-; before vowels n-; older and in poetry in-. The n form is also frequently used after a preceding vowel, as: i·lambe “the tongue”; i·noldoli “the gnomes”; i·lambe’n·noldolion “the tongue of the gnomes”. The definite article is indeclinable (PE14/42).
DEFINITE ARTICLE. i·, before vowels n· (older and in poetry in·). The n form is also frequently used after a preceding vowel, as: i·lambe “the tongue”; i·noldoli “the gnomes”; i·lambe n·noldolion “the tongue of the gnomes”. THE DEFINITE ARTICLE IS INDECLINABLE (PE14/71).
These variant n- definite articles appear fairly often in Tolkien’s early writing (PE15/32; PE16/62, 72, 74, 77), but by the 1930s they had disappeared. There is no mention of n- or in articles after that, except for one late example from the 1950s: i·coimas in·Eldaron (PM/403). This might be transient restoration of the paradigm from the 1920s, but without more examples it has hard to be sure.
The Early Qenya Grammar from the 1920s also had an indefinite article in the form of the suffix ᴱQ. -ma:
Indefinite article. “a”, in pl. “some, certain”, is suffixed -ma. Trissyllabic nouns of which the penultimate syllable is short, lengthen the final vowel, as: tantare “dance”; tantaré·ma “a dance”.
Consonantal nouns usually allow the full stem, as in declension, to reappear. The form of the article is then -uma, as: peltas (pl. peltaksi) “pivot”: peltaks·uma.
Occasionally after l, r, n a shorter form is used, as: kaimasan “bed-chamber”: kaimasam·ma, or kaimasamb·uma; wingil “sea-nymph”: wingil(d·u)ma.
This -ma is declined like ordinary adjectives, q.v. (PE14/42).
The typescript version (PE14/71) has the same set of rules and examples. There is no sign of this suffix from the 1930s forward; later on -ma was mostly used as an instrumental suffix.