The Sindarin imperative is surprisingly straightforward: simply add -o to a basic verb, or change the final -a of a derived verb to -o, in order to indicate a command. Examples are numerous:

• noro lim, noro lim Asfaloth “run swift, run swift, Asfaloth” (LotR/213; PE17/18).
• pedo mellon a minno “speak, friend, and enter” (LotR/305).
• fennas nogothrim, lasto beth lammen “doorway of the Dwarf-folk listen to the word of my tongue” (LotR/307; PE17/45).
• annon edhellen, edro hi ammen “Elvish gate open now for us” (LotR/307; PE17/45).
• a tiro nin, Fanuilos “o guard me, Elbereth” (LotR/729; RGEO/64).
• cuio i Pheriain anann “may the Halflings live long” (LotR/953; Let/308).
• Lacho calad! Drego morn! “Flame light! Flee night!” (UT/65).
• no aer i eneth lín “hallowed be thy name” (VT44/21).
• tolo i arnad lín “thy kingdom come” (VT44/21).
• caro den i innas lin “thy will be done” (VT44/21).
• anno ammen sír i mbas ilaurui vín “give us this day our daily bread” (VT44/21).
• ar díheno ammen i úgerth vin “and forgive us our trespasses” (VT44/21).

The Sindarin imperative is typically used for commands: noro lim “run swift”. However, it may also be used for the expression of a wish: cuio i Pheriain anann “live the Halflings long (may the Halflings live long)”; no aer i eneth lín “be hallowed thy name (hallowed be thy name)”. In such expressions, the putative subject of the wish follows the imperative, since the imperative always appears at the beginning of the phrase.

Tolkien described the historical origin of Sindarin imperative in a couple places:

The o of Sindarin “imperative” is an agglutination of the exclamation ā! found separately in Quenya before or after the bare tense stem when used “imperatively” (from a 1955 draft letter to David Masson, PE17/40).

ā the imperative particle, being originally independent and variable in place, survived in S as ō > o, though this now always followed the verb stem and had become an inflexion (Quendi and Eldar, circa 1960, WJ/365).

It seems the ancient long ā followed its typical development in polysyllables: ā > ǭ > o. This development indicates the agglutination was not ancient, since the long ā did not shorten as it generally did at the end of words. Thus at least ā > ǭ before it was agglutinated to the verb and became inflectional.

Negative Imperative: A negative imperative in Sindarin is formed with the adverb avo, itself the imperative of the ancient verb ava- that survived only in a few fossilized forms. As Tolkien described it:

avo negative adverb with verbs, as avo garo! “don’t do it”; sometimes used as a prefix: avgaro (< *aba-kar ā). This could be personalized in the form avon “I won’t”, avam “we won’t”: these were of course not in fact derived from avo, which contained the imperative -o < *ā, but from the verb stem *aba, with inflexions assimilated to the tense stems in -a; but no other parts of the verb survived in use, except the [verbal] noun avad “refusal, reluctance” ... With the uses of this stem, primary meaning “refuse, be unwilling”, to form negative imperatives, cf. Latin nōlī, nōlīte [there is a similar Latin formation for negative imperatives] (WJ/371-372).

The adverb avo is followed by the verb in the imperative form, in a sense forming a “double imperative”: avo mado “don’t eat”. Sindarin also has a “curt imperative” baw “don’t!”, always used by itself (not followed by another verb):

In Sindarin the following forms are found, baw! imperious negative: “No, no! Don’t!” ... Derived direct from baw! (*bā) was the verb boda- “ban, prohibit” (*bā-ta) (WJ/371-372).

For further information on the other forms like avon “I won’t”, see the discussion of the negative.

Conceptual Development: There is no mention of the imperative in either the Gnomish Grammar of the 1910s or the Early Noldorin Grammar of the 1920s. Imperatives do appear in The Etymologies, but all the examples are of verbs that appear in The Lord of the Rings: [N.] daro, edro, tiro (Ety/DAR; Ety/ETER; EtyAC/NDI). I think these were probably later additions to The Etymologies from the 1940s, while Tolkien was working on Lord of the Rings drafts.

The first imperative to appear in Lord of the Rings drafts had a slightly different form:

• [N.] nora-lim, nora-lim “*run swift, run swift” (RS/196).

This imperative used the suffix -a rather than -o. But Tolkien switched to -o by the time he first wrote pedo mellon a minno (TI/182). He stuck with this formation thereafter.