The grammar of verbs in Proto-Indo-European (PIE) differs markedly from its modern descendants, although many properties of the old system remain.
PIE verbs were inflected for aspect, voice, mood, tense, person and number. However, not all possible combinations existed.
Unlike most modern languages, which organise the verbs primarily by tense (the time of occurrence), PIE verbs were primarily based on aspect (the flow of time throughout the action). PIE verbs had three aspects:
Each aspect had its own inflectional stem, which followed a unique conjugational pattern and could not be predicted from the root nor the conjugation for the other aspects of the verb. Many verb roots were also defective, and had stems only for one or two of the aspects. More strikingly, there were also a few verbs that had more than one set of forms for the same aspect; for example the root *ǵneh₃- (“to recognise, to know”) had two present stems and two aorist stems. This is strong evidence that the verb stems used for each aspect were originally independent verbs, and that the relationship between them was derivational rather than inflectional. Consequently, the later process by which the aspects were combined into unified paradigms was in origin a form of suppletion. This explains why some verbs like Latin sum and ferō have different stems for different tenses. The case of English be is even more unusual, as it was formed from two separate present tense paradigms (beeth and is) that shared the same past tense paradigm (was).
Voice indicates the relationship between the verbal action and its subject. PIE had two voices:
Voice was distinguished only in the present and aorist aspects. The perfect did not have a distinction in voice, which presumably was a result of its stative (hence intransitive) meaning.
The mood of a verb indicates the way in which the speaker perceives an event, or what their attitude towards it is. PIE distinguished the following moods:
These four moods existed for all three aspects and for both the active and mediopassive voice. The indicative mood of the present aspect additionally distinguished between two tenses (see below). Therefore, a 'full' verb paradigm that had all three aspects (such as *leykʷ-) would have had seven distinct indicative forms for each person-and-number combination (four in the present aspect, two in the aorist, one in the perfect).
Tense was distinguished only for the present aspect, and only for the indicative mood. The aorist and perfect aspects did not have tenses, nor did the subjunctive, optative or imperative moods.
In the present aspect, there was a difference between the present and imperfect tense (not to be confused with the present and imperfective/aorist aspect). The present tense indicated events that were happening at the moment of speaking, while the imperfect tense indicated an event happening in the past. The imperfect tense of the present aspect differed from the aorist aspect in that the aorist aspect indicated events without reference to the internal structure of the event, while the imperfect tense, being part of the present aspect, did imply this information. Furthermore, the aorist aspect also had subjunctive, optative and imperative moods, which could be used (and judging from Greek usage, often were) with present meaning.
Person and number were not distinguished separately but always as a combination of the two. There were three persons (first, second and third) like in most languages, and three numbers (singular, dual and plural). The first person did not exist in the imperative mood.
The following is a list of known reconstructible formations for stems of each aspect.[1] They are divided between stems that follow the athematic inflection and stems that follow the thematic inflection.
Present stem formations distinguished between primary and secondary stem formations. Primary stems were formed directly from roots and typically had basic verbal meanings. Secondary stems were formed from other stems, such as nouns, adjectives or even from other verbs. Primary stems often had corresponding aorist and/or perfect stems, while secondary stems never did (this fact led to the creation of the 'weak verbs' in the Germanic languages). Note that primary verb roots rarely formed both a root present and a root aorist, as these formations were identical (at least for the present imperfect) and thus easily confused. It is possible that a similar rule prevented a verb root from forming both a thematic present and a thematic aorist, too.
Athematic:
Thematic:
Athematic:
Thematic:
All perfect stems were athematic.
| Imperfective, thematic | |||||
|---|---|---|---|---|---|
| 3rd singular | *-eti | ||||
| 3rd plural | *-onti | ||||
| Active voice | Present indicative | Past indicative | Imperative | Subjunctive | Optative |
| 1st singular | *-oh₂ | *-om | — | *-ōh₂ | *-oyh₁m̥ |
| 2nd singular | *-esi | *-es | *-e | *-ēsi | *-oys |
| 3rd singular | *-eti | *-et | *-etu | *-ēti | *-oyt |
| 1st dual | *-owos | *-owe | — | *-ōwos | *-oywé |
| 2nd dual | *-etes | *-etom | *-etom | *-ētes | *-oytóm |
| 3rd dual | *-etes | *-etām | *-etām | *-ētes | *-oytā́m |
| 1st plural | *-omos | *-ome | — | *-ōmos | *-oymé |
| 2nd plural | *-ete | *-ete | *-ete | *-ēte | *-oyté |
| 3rd plural | *-onti | *-ont | *-ontu | *-ōnti | *-oyh₁ént |
| Participle | *-oónts | ||||
| Middle voice | Present indicative | Past indicative | Imperative | Subjunctive | Optative |
| 1st singular | *-oh₂er | *-oh₂e | — | *-ōh₂er | *-oyh₂é |
| 2nd singular | *-eth₂er | *-eth₂e | *-eso | *-ēth₂er | *-oyth₂é |
| 3rd singular | *-etor | *-eto | *? | *-ētor | *-oytó, *-oyh₁ó |
| 1st dual | *-owosdʰh₂ | *-owedʰh₂ | — | *-ōwosdʰh₂ | *-oywédʰh₂ |
| 2nd dual | *? | *? | *? | *? | *? |
| 3rd dual | *? | *? | *? | *? | *? |
| 1st plural | *-omosdʰh₂ | *-omedʰh₂ | — | *-ōmosdʰh₂ | *-oymédʰh₂ |
| 2nd plural | *-edʰh₂we | *-edʰh₂we | *-edʰh₂we | *-ēdʰh₂we | *-oydʰh₂wé |
| 3rd plural | *-ontor | *-onto | *? | *-ōntor | *-oyró |
| Participle | *-omnós | ||||
| Imperfective, athematic | |||||
|---|---|---|---|---|---|
| 3rd singular | *-ti | ||||
| 3rd plural | *-énti | ||||
| Active voice | Present indicative | Past indicative | Imperative | Subjunctive | Optative |
| 1st singular | *-mi | *-m̥ | — | *-oh₂ | *-yéh₁m̥ |
| 2nd singular | *-si | *-s | *-, *-dʰí | *-esi | *-yéh₁s |
| 3rd singular | *-ti | *-t | *-tu | *-eti | *-yéh₁t |
| 1st dual | *-wós | *-wé | — | *-owos | *-ih₁wé |
| 2nd dual | *-tés | *-tóm | *-tóm | *-etes | *-ih₁tóm |
| 3rd dual | *-tés | *-tā́m | *-tā́m | *-etes | *-ih₁tā́m |
| 1st plural | *-mós | *-mé | — | *-omos | *-ih₁mé |
| 2nd plural | *-té | *-té | *-té | *-ete | *-ih₁té |
| 3rd plural | *-énti | *-ént | *-éntu | *-onti | *-ih₁ént |
| Participle | *-ónts | ||||
| Middle voice | Present indicative | Past indicative | Imperative | Subjunctive | Optative |
| 1st singular | *-h₂ér | *-h₂é | — | *-oh₂er | *-ih₁h₂é |
| 2nd singular | *-th₂ér | *-th₂é | *-só | *-eth₂er | *-ih₁th₂é |
| 3rd singular | *-tór, *-ór | *-tó, *-ó | *? | *-etor | *-ih₁tó, *-ih₁ó |
| 1st dual | *-wósdʰh₂ | *-wédʰh₂ | — | *-owosdʰh₂ | *-ih₁wédʰh₂ |
| 2nd dual | *? | *? | *? | *? | *? |
| 3rd dual | *? | *? | *? | *? | *? |
| 1st plural | *-mósdʰh₂ | *-médʰh₂ | — | *-omosdʰh₂ | *-ih₁médʰh₂ |
| 2nd plural | *-dʰh₂wé | *-dʰh₂wé | *-dʰh₂wé | *-edʰh₂we | *-ih₁dʰh₂wé |
| 3rd plural | *-n̥tór, *-rór | *-n̥tó, *-ró | *? | *-ontor | *-ih₁ró |
| Participle | *-m̥h₁nós | ||||
| Perfective, thematic | ||||
|---|---|---|---|---|
| 3rd singular | *-et | |||
| 3rd plural | *-ont | |||
| Active voice | Indicative | Imperative | Subjunctive | Optative |
| 1st singular | *-om | — | *-ōh₂ | *-oyh₁m̥ |
| 2nd singular | *-es | *-e | *-ēsi | *-oys |
| 3rd singular | *-et | *-etu | *-ēti | *-oyt |
| 1st dual | *-owe | — | *-ōwos | *-oywé |
| 2nd dual | *-etom | *-etom | *-ētes | *-oytóm |
| 3rd dual | *-etām | *-etām | *-ētes | *-oytā́m |
| 1st plural | *-ome | — | *-ōmos | *-oymé |
| 2nd plural | *-ete | *-ete | *-ēte | *-oyté |
| 3rd plural | *-ont | *-ontu | *-ōnti | *-oyh₁ént |
| Participle | *-oónts | |||
| Middle voice | Indicative | Imperative | Subjunctive | Optative |
| 1st singular | *-oh₂e | — | *-ōh₂er | *-oyh₂é |
| 2nd singular | *-eth₂e | *-eso | *-ēth₂er | *-oyth₂é |
| 3rd singular | *-eto | *? | *-ētor | *-oytó, *-oyh₁ó |
| 1st dual | *-owedʰh₂ | — | *-ōwosdʰh₂ | *-oywédʰh₂ |
| 2nd dual | *? | *? | *? | *? |
| 3rd dual | *? | *? | *? | *? |
| 1st plural | *-omedʰh₂ | — | *-ōmosdʰh₂ | *-oymédʰh₂ |
| 2nd plural | *-edʰh₂we | *-edʰh₂we | *-ēdʰh₂we | *-oydʰh₂wé |
| 3rd plural | *-onto | *? | *-ōntor | *-oyró |
| Participle | *-omnós | |||
| Perfective, athematic | ||||
|---|---|---|---|---|
| 3rd singular | *-t | |||
| 3rd plural | *-ént | |||
| Active voice | Indicative | Imperative | Subjunctive | Optative |
| 1st singular | *-m̥ | — | *-oh₂ | *-yéh₁m̥ |
| 2nd singular | *-s | *-, *-dʰí | *-esi | *-yéh₁s |
| 3rd singular | *-t | *-tu | *-eti | *-yéh₁t |
| 1st dual | *-wé | — | *-owos | *-ih₁wé |
| 2nd dual | *-tóm | *-tóm | *-etes | *-ih₁tóm |
| 3rd dual | *-tā́m | *-tā́m | *-etes | *-ih₁tā́m |
| 1st plural | *-mé | — | *-omos | *-ih₁mé |
| 2nd plural | *-té | *-té | *-ete | *-ih₁té |
| 3rd plural | *-ént | *-éntu | *-onti | *-ih₁ént |
| Participle | *-ónts | |||
| Middle voice | Indicative | Imperative | Subjunctive | Optative |
| 1st singular | *-h₂é | — | *-oh₂er | *-ih₁h₂é |
| 2nd singular | *-th₂é | *-só | *-eth₂er | *-ih₁th₂é |
| 3rd singular | *-tó, *-ó | *? | *-etor | *-ih₁tó, *-ih₁ó |
| 1st dual | *-wédʰh₂ | — | *-owosdʰh₂ | *-ih₁wédʰh₂ |
| 2nd dual | *? | *? | *? | *? |
| 3rd dual | *? | *? | *? | *? |
| 1st plural | *-médʰh₂ | — | *-omosdʰh₂ | *-ih₁médʰh₂ |
| 2nd plural | *-dʰh₂wé | *-dʰh₂wé | *-edʰh₂we | *-ih₁dʰh₂wé |
| 3rd plural | *-n̥tó, *-ró | *? | *-ontor | *-ih₁ró |
| Participle | *-m̥h₁nós | |||
| Stative | ||||
|---|---|---|---|---|
| 3rd singular | *-e | |||
| 3rd plural | *-ḗr | |||
| Active voice | Indicative | Imperative | Subjunctive | Optative |
| 1st singular | *-h₂e | — | *-oh₂ | *-yéh₁m̥ |
| 2nd singular | *-th₂e | *-, *-dʰí | *-esi | *-yéh₁s |
| 3rd singular | *-e | *-tu | *-eti | *-yéh₁t |
| 1st dual | *-wé | — | *-owos | *-ih₁wé |
| 2nd dual | *? | *-tóm | *-etes | *-ih₁tóm |
| 3rd dual | *? | *-tā́m | *-etes | *-ih₁tā́m |
| 1st plural | *-mé | — | *-omos | *-ih₁mé |
| 2nd plural | *-é | *-té | *-ete | *-ih₁té |
| 3rd plural | *-ḗr | *-éntu | *-onti | *-ih₁ént |
| Participle | *-wṓs | |||