Old Irish class A III verbs (McCone's hiatus verbs H1, H2, and H3) have a present stem that ends in a vowel; they are derived from Proto-Celtic verbs whose present stems ends in s, w, or y.
Absolute forms are not widely attested in this class; many of the forms given below are hypothetical.
McCone's class H1 comprises hiatus verbs whose stem ends in a or á. A sample verb for this class is ráïd(“to row”), but as that verb is not widely attested, at·tá(“to be”) provides a large complement of present conjunct forms. The endings are as follows:
McCone's class H2 comprises hiatus verbs whose stem ends in i or í. A sample verb for this class is gníïd(“to do, make”), whose conjunct forms are attested especially well in do·gní. This subclass has a tendency to take on their own unique subjunctive formation, the e-subjunctive.
The endings are as follows:
Present indicative
1st sg.
2nd sg.
3rd sg.
1st pl.
2nd pl.
3rd pl.
Passive singular
Passive plural
Absolute
gníu*
gní
gníid
gnímmi
unattested; presumably *gníthe
gníit
gníthir
gnítir
Conjunct
·gníu*
·gní
·gní
·gniäm
·gníith
·gniät
·gníther
·gníter
Relative
gnís†
gnímme
gníte
gníther
gníter
*The ending -im is found in (·)liïm (from liïd) and in the prototonic form of some complex verbs such as ·dénaim from do·gní and ·accim from ad·cí.
McCone's class H3 comprises hiatus verbs whose stem ends in other vowels. Sample verb for this class include foïd(“to spend the night”), soïd(“to turn”), and sceïd(“to vomit”), as well as conjunct forms from ad·noí(“to entrust”), con·oí(“to protect”), and as·luí(“to escape”). The endings are as follows:
Apparently only class H3 deponent verbs are attested. Sample verbs for this class are luïthir(“to move”) and con·oathar(“to protect”). The endings are as follows:
