The accusative form in Quenya is used for the object of verbs and is unmarked in “modern” Quenya (Tarquesta). According to the Plotz letter, there was a distinct accusative form in Classical Quenya (Parmaquesta), marked with a long final vowel in the singular, and by the use of an -i plural for vocalic nouns in the plural:
Totally off topic, but Sir Ian McKellen is 80 and tours the world with a one-man show celebrating his long career - I saw him the other day in London, and (naturally) he started the show by reciting the Bridge of Khazad-dûm scene from The Fellowship :) and afterwards he produced the actual Glamdring he used as a prop in the films and brandished it around the stage.
There was much more in the show of course, and he is a lovely man. A great night.
Like most languages, Quenya distinguishes between singular (one) and plural (multiple) nouns. Quenya has two special plural forms, the dual (for pairs) and the partitive plural (for portions of groups = “some”). This entry discusses the general plural, which is used for all the other forms of noun plurality.
A couple of months ago @Paul Strack posted a short but neat analysis of the attested Quenya particles of uncertainty, their possible shades of meaning and use. Since Discord is a platform we cannot link to, I am copying the text here, for further discussion, and to preserve it for posterity:
ma = interrogative/indefinite (probably true)
qui = neutral hypothetical (may or may not be true)
ai/ce = strong hypothetical (probably not true)
In addition to the “general” plural, Quenya has a special “partitive” plural used when describing a portion of a group. The partitive plural is formed using the suffix -li, variously translated as “some, many, a lot of” (PE17/62, 127, 135; VT47/12). It is derived from the primitive root √LI “many” (Ety/LI, VT48/25). Tolkien described the use of this suffix on several occasions:
Like English, Quenya has singular and plural nouns, with singular unmarked and plural marked by -i or -r. However, Quenya has two additional “special plurals”, the dual used when there are only two of an item (“both”), and the partitive-plural when the plural represent a subset of a larger group (“some”). Thus: