The i-future, which is found in verbs belonging to conjugation classes B IV or A III, is characterized by a reduplication of the initial consonant with the vowel i. It lacks the suffix -s- of the s future, which is why it called an asigmatic future.
The initial consonant of the root is of course lenited after the i of the reduplicating syllable.
The future stem is used to form the conditional tense (called “secondary future” in some sources including Thurneysen and Strachan) as well as the future itself.
See Category:Old Irish i future verbs for a list of verbs that take the i-future.
The basic pattern shows a reduplicating syllable with the vowel i (the n is part of the present stem only and so is not found in the future stem):
When the stem begins with a velar stop followed by a liquid consonant, the i and the following consonant combine to form the diphthong íu:
In the verb ·fen (and, by analogy, benaid), the consonant after the reduplicating syllable is lenited out of existence; since there are no other consonants in the stem, the future stem is nothing but the reduplicating syllable with a lengthened vowel:
The attested endings are as follows:
| 1st sg. | 2nd sg. | 3rd sg. | 1st pl. | 2nd pl. | 3rd pl. | Passive singular | Passive plural | |
|---|---|---|---|---|---|---|---|---|
| Absolute | ciche* | lile† | lilith | — | — | lilit | — | — |
| Conjunct | ·bíu | — | ·riri | — | — | ·cíurat | ·rirther | — |
| Relative | liles | — | — | — | — |
* A late form presumably for earlier *cichiu.
† Possibly for earlier *lili
| 1st sg. | 2nd sg. | 3rd sg. | 1st pl. | 2nd pl. | 3rd pl. | Passive singular | Passive plural |
|---|---|---|---|---|---|---|---|
| — | — | ·gíulad | — | — | — | fo·indarpaide | — |
There are no deponent verbs that take the i-future.