Old Irish object pronouns are affixes attached to the verb. There are both suffixed pronouns and prefixed pronouns, of which latter are usually called “infixed pronouns” since they are inserted between a preverb and the verb and can never be the first morpheme in the verbal complex.
The suffixed pronouns are suffixed to absolute forms of simple active verbs only. In all other cases the infixed pronouns are used. The following forms are used only after 3rd person singular verb forms:
| Person | Singular | Plural |
|---|---|---|
| 1 | -um | -unn |
| 2 | -ut | -uib |
| 3 m. & n. | -i | -us |
| 3 f. | -us |
Because a suffixed pronoun is typically added as an odd-numbered syllable, the preceding verb undergoes regular syncopation, i.e. loss of short vowels in even-numbered non-final syllables. The result of this syncopation is that the early Old Irish 3rd person singular present-tense ending -(a)ith (with regular voicing of word-final -th in polysyllablic words to -d in later Old Irish) being reduced to -th- (which is regularly delenited to -t- /t/ after a non-rhotic coronal consonant, i.e. s t d n l, but not r), and the -(a)is ending of the preterite is reduced to -s-. For example:
In addition to the above, the 3rd person singular masculine/neuter suffixed pronoun -it can be found:
Despite the name, the infixed pronouns are technically prefixes rather than infixes as they always precede the entire root. However, they follow both preverbal particles and other prefixes, including those prefixes that are lexically part of the verb, e.g. do·gníu (“I do”) with an “infixed pronoun” becomes da·gníu (“I do it”). If no other preverb or prefix is available, they are attached to the “dummy preverb” no-.
There are three classes of infixed pronoun: class A, class B, and class C. Classes B and C are identical except in the 3rd person singular masculine and neuter.
| Person | Class A | Class B | Class C |
|---|---|---|---|
| 1 sing. | m-L | dom-L, dam-L | |
| 2 sing. | t-L | dot-L, dat-L, dut-L, dit-L | |
| 3 sing. m. | a-N, e-N | d-N | id-N, did-N, d-N |
| 3 sing. f. | s-(N) | da- | |
| 3 sing. n. | a-L, e-L | d-L | id-L, did-L, d-L |
| 1 pl. | n- | don-, dun-, dan- | |
| 2 pl. | b- | dob-, dub-, dab- | |
| 3 pl. | s-(N) | da- | |
| L means this form triggers lenition. N means this form triggers nasalization (eclipsis) (N) means this form triggers nasalization in some texts but not in others. | |||
Class A infixed pronouns are used after prefixes that were originally vowel-final: ro-, no-, dí-, to-, fo-, ar-, and imm-, as well as the negative particle ní. The prefixes ro-, no-, di-, to-, and fo- lose their vowel before 3rd sing. m./n. a-, while a- itself disappears after ní, leaving only its mutation effect. The prefixes ar- and imm- take an epenthetic vowel (usually -u- or -i-) before the class A infixed pronouns that start with a consonant.
Class B infixed pronouns are used after prefixes that were originally consonant-final: ad-, aith-, com-, ess-, etar-, for-, fris-, and in-. The prefixes ad-, aith-, ess-, and in- all merge with the following pronoun to become atom-, atot-, etc.; com- merges with the pronoun to become cotom-, cotot-, etc.; and fris- merges with the pronoun to become fritom-, fritot-, etc.
Class C infixed pronouns are used:
In many of these contexts, the infixed pronoun undergoes nasalization, so that the initial d- appears as nd- or even n-. In relative clauses, ess- and frequently also ad-, aith-, and in-, merge with the third-person pronouns to become as(s)id-/as(s)ind-/as(s)in-; co (“so that”) merges with it to become condid-/conid-; fris- merges with it to become fris(s)id-/fris(s)ind-/fris(s)in-; tri- merges with it to become tres(s)ind-/tris(s)ind-.