Tolkien often distinguished verb conjugations (for the various verb tenses: aorist, present, past, perfect, future) from what he called “verb inflections”. These inflections are added to the tense stem, and came in three types:

• The subject suffixes: -n(ye), -l(ye), -s etc.
• The object suffixes: -s, -t.
• Agreement for number: plural -r or dual -t.

The subject suffixes are used in cases when the subject is not an independent noun, and marks the subject of the sentence: matin(ye) “I eat”, matis “he/she eats”. They are not used if there is a separate subject, including emphatic pronouns: i atan mate “the man eats”, elye mate “even you eat”. The object suffixes are only used for 3rd person singular (him/her/it) and plural (them) object pronouns, and may be added after the (long) subject suffixes: matinyes “I eat it”, cennelyet “you saw them”. Both the subject suffixes and object suffixes are discussed in more detail in their own entries.

The object suffixes may be (more rarely) attached to the verb with a separate (or no) subject: emme apsenet “we forgive them” (VT43/20); nai nin híres “it may well chance for me to find it, *(lit.) may it be for me that it is found” (PE22/151). Based on these two examples, it seems that when an object suffixes is added to an aorist verb, the vowel remains e rather that the more usual i that appears in most inflected aorist forms. Thus matis “he/she eats” but i atan mates “the man eats it”. Hat tip to Shihali for pointing this out to me.

In cases where there is a separate singular subject, the verb is uninflected. However, if the subject noun is dual or plural, the verb must also be dual or plural to agree in number with the subject using the suffixes -t and -r. Tolkien generally labeled these the “impersonal” inflections, and they appeared in various inflectional charts in the 1960s (PE17/57, 75; VT49/16, 51). Some examples:

• nai elen atta siluvat aurenna veryanwesto “*may two stars shine upon the day of your wedding” (VT49/44); sil-uva-t = “shine-(future)-(dual)”.
• lassi lantar laurie súrinen “leaves fall golden in the wind” (RGEO/58); lanta-r = “fall-(plural)”.

It is less clear whether the plural agreement is required for an independent pronominal subject. We have only one example, emme apsenet “we forgive them” from the Átaremma prayer of the 1950s (VT43/20), where a plural pronoun (emme “we”) does not have a plural verb (apsene rather than apsenir). In earlier drafts of the prayer, Tolkien experimented with various forms trying to figure out how the plural suffix combined with a 3rd person plural object: avatyarirat >> avatyarir ta >> avatyarilta (using a different verb avatyar- for “forgive”). For purposes of Neo-Quenya, I think it is safer to assume plural emphatic pronoun subjects would use plural agreement in the verb: *elme apsenir te.

Origin of impersonal plural and dual suffixes: The impersonal plural suffix -r dates back to Common Eldarin; it also appears in Sindarin. Its original CE form was probably l, however:

Plurality ... As final affixes, originally probably not used before other affixes or inflexions, but if appearing with these at all added on to them at the end, there appeared (a) m chiefly substantival; (b) r, l especially used in verbs as the plural of the indeterminate (genderless or impersonal) form (Primitive Quendian Structure: Final Consonants, 1936, PE21/56-57).

... final consonantal elements ... l > r at an early period: the plural indicator r (in CE only attached to otherwise uninflected verbal stems, but much extended in PQ) is probably derived from l (Outline of Phonology, OP2, around 1950s, PE19/103).

r (more rarely l) was originally, it seems, employed chiefly in verbs to mark the plural subject, especially when this was unspecified or indeterminate (Common Eldarin: Noun Structure, early 1950s, PE21/73).

Remnants of the verbal l-plural can be seen in the pronominal subject suffixes, many of which are of the form l + independent pronoun: -lme “we” = -l + me, -lde “you” = -l + de, -lte “they” = -l + te (VT49/51). In Quenya, the verbal r-plural was transferred to nouns, where it became the usual suffix for plural nouns ending in a vowel.

It is a bit less clear how the verbal dual suffix arose. Tolkien mentioned ancient verbal duals in a couple places:

Duality ... As final affixes appeared s, t, th (choice varying in different languages), of which s often appeared medially, especially in verbal inflexion, before other affixes (Primitive Quendian Structure: Final Consonants, 1936, PE21/57).

Duality ... But the elements {s, t >>} s, th competed with it and could in CE be used in noun-declension as well as verbal, and could precede other affixes (Common Eldarin: Noun Structure, early 1950s, PE21/73).

Thus it seems there were several competing dual suffixes for verbs in CE. Meanwhile, in nouns the suffix -t became the usual dual suffix for nouns ending a vowel, developed as a reduction of ✶ata “two” (Let/427). Perhaps this noun dual help normalize the dual form of verbs. The verbal t-dual may even have been borrowed from nouns, the reverse of the r-plural borrowing.

Conceptual Development: The “impersonal” verb inflections date all the way back to The Qenya Verb Forms of the 1910s, which had impersonal dual -t and plural -r (PE14/28). In the Early Qenya Grammar (EQG) of the 1920s, -l was the verbal plural suffix, and was used with plural pronominal subject prefixes:

-l for plural, as: me·tulil “we come” (PE14/56).

In the typescript version of EQG, Tolkien also had a few examples of agreement with dual pronouns, using verbal dual suffixes -s or -t: muyantas = mu-yanta-s “*(we-two)-give-(dual)”, muyanyet = mu-yanye-t “*(we-two)-gave-(dual)” (PE14/86). In the Qenya Conjugations of the late 1920s or early 1930s, the impersonal suffixes were -r dual and -l or -nt plural (PE16/124-125).

By the 1930s and 40s the verbal r-plural and t-dual again became the norm, with remnants of the more ancient l-plural in pronominal suffixes, as described above. In the Quenya Verbal System written in the late 1940s, Tolkien went through a (brief) period where he restored pronominal subject prefixes, and pronominal suffixes were limited to objects. This meant that it was more likely that a plural verb would also have an object suffix, and these combinations seemed to likewise preserve ancient verbal l-plurals, such as:

• ᴹQ. me·nakilti “we hate them” (PE22/112).
• ᴹQ. me·merilti karilthi “we wish them to make them (other things)” (PE22/118).

Here the verbs are plural to agree with their plural subject (me “we”), but also have an object suffix (ti “they”) which preserved the ancient l-plural and prevented it from becoming -r: nakilti = nak-i-l-ti “hate-(aorist)-(plural)-them”, merilti = mer-i-l-ti “wish-(aorist)-(plural)-them”. Something like this is also seen in some versions of the 1950s Átaremma prayer: avatyarilta, presumably avatyar-i-l-ta “forgive-(aorist)-(plural)-those” as suggested by Wynne, Smith and Hostetter (VT43/10-11, 20). More forms like this appear in related notes, where Tolkien had carita, carilta, carires and [deleted] caris (VT43/25-26, note #5). As suggested by Wynne, Smith and Hostetter, these are presumably:

• Aorist singular with plural object: car-i-ta “*do-(aorist)-those”.
• Aorist plural with plural object: car-i-l-ta “*do-(aorist)-(plural)-those”.
• Aorist plural with singular object: car-i-r-es “*do-(aorist)-(plural)-it”.
• Aorist singular with singular object: car-i-s “*do-(aorist)-it” [deleted].

The last of these was deleted, probably because it was identical to the aorist with a 3rd-singular pronoun: caris “he/she does”; the object-form should perhaps be cares (see above).

Neo-Quenya: For purposes of Neo-Quenya, I would avoid agglutinating an object suffix to a plural or dual verb form, keeping the pronoun separate instead: atani cenir te “man-(plural) see-(aorist)-(plural) them”, atanu carit sa “man-(dual) do-(aorist)-(dual) it”. As interesting as the verbal l-plural with object suffix syntax is, Tolkien seems to have been uncertain of it, and we have no idea what the dual formation might be.

However, I think it is fine to agglutinate object pronouns to singular verbs, since (a) there are several attested examples in Tolkien’s later writing and (b) the meaning would be clear from the independent subject noun: mantes “he/she ate” vs. i atan mantes “the man ate it”. As suggested above, the object suffixes by themselves would not preserve the ancient i when attached to aorist verbs, so i atan cenet, i atan cenes “the man sees them, the man sees him/her/it” vs. cenis “he saw”.