Appendix:Proto-Indo-European verbs

The grammar of verbs in Proto-Indo-European (PIE) differs markedly from its modern descendants, although many properties of the old system remain.

Inflectional categories
PIE verbs were inflected for aspect, voice, mood, tense, person and number. However, not all possible combinations existed.

Aspect
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:


 * Present (imperfective) aspect: Indicated actions that have internal structure in time, such as being continuous, habitual, ongoing, unfinished. The present aspect was the only of the three aspects to have a distinction between present and past tense.
 * Aorist (perfective) aspect: Indicated actions that have no internal structure, and was used when the speaker was not interested in such details. The time of speaking imposes internal structure, as something happening in the present is by definition ongoing. Therefore, the aorist aspect did not have a present tense.
 * Perfect (stative) aspect: Indicated not an action or event, but the state resulting from an action. As such a state implies a past action, it often became used in the descendants of PIE for the past tense.

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 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 and  have different stems for different tenses. The case of English is even more unusual, as it was formed from two separate present tense paradigms ( and ) that shared the same past tense paradigm.

Voice
Voice indicates the relationship between the verbal action and its subject. PIE had two voices:


 * The active voice, used when the subject of the verb was the agent of the verb, who was performing the action (on the direct object).
 * The mediopassive or middle voice, when the subject and direct object are not distinguishable. Often, the mediopassive voice indicated actions performed by the subject on itself (reflexive), two subjects on each other (reciprocal), or on no object at all.

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.

Mood
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:


 * The indicative mood, for statements of (perceived) fact or reality.
 * The subjunctive mood, for hypothetical statements which were not perceived as actual. This included especially future events.
 * The optative mood, for statements of wish or hope.
 * The imperative mood, for direct commands and orders. This mood was not used in the first person.

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 ) 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
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
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.

Aspect stems
The following is a list of known reconstructible formations for stems of each aspect. 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.

Present stems
Athematic:
 * Root present: The plain verbal root, with no affixes.
 * Normal root present: Full ablaut grade and accent on the root in the singular, zero grade and accent on the ending in the nonsingular. This type was analogous to the alternating root nouns. Example:.
 * Narten present: Lengthened grade in the singular, full grade in the nonsingular, with accent always on the root. This type was analogous to the acrostatic root nouns. Example:.
 * Reduplicated athematic present: The first consonant of the root was repeated, with an extra intervening vowel. Ablaut variations were as in normal root presents, but the accent was fixed on the extra vowel.
 * With vowel -e-. Example:.
 * With vowel -i-. Example:.
 * Nasal infix present: The alternating infix -né- ~ -n̥- was inserted before the last consonant of the zero-grade form of the root. Ablaut and accent variations were as in normal root presents, but affected the infix rather than the root. Example:.
 * Athematic present with suffix -néw- ~ -nu-. The suffix was added at the end of the zero-grade form of the root. Ablaut and accent variations were as in normal root presents, but affected the suffix rather than the root. Example:.
 * Stative present (secondary) with suffix -éh₁-. Formed from adjectival and nominal roots (so-called 'Caland roots'). The suffix was added to the zero-grade form of the root, and was always accented and in the full grade. It was originally athematic (as in Anatolian) but in later PIE the thematic denominative -yé/ó- suffix was added, creating a compound -eh₁yé/ó- suffix. Example:.
 * Factitive present (secondary) with suffix -eh₂-. Formed from thematic adjective stems, and probably inherited their accent and stem ablaut. This suffix was likewise originally athematic but the thematic denominative -yé/ó- suffix was added in later PIE, resulting in -eh₂yé/ó-, which became very productive in almost all descendants. Example:.

Thematic:
 * Simple thematic present: The thematic vowel was added to the root, which was normally -o-, but -e- when it was followed by s, t, d or dʰ.
 * Normal thematic present: Accented on the root, with the root in full grade. Example:.
 * Tudati-present: Accented on the thematic vowel, with the root in zero grade. The name comes from Sanskrit, a verb which is representative of this type. Example:.
 * Reduplicated thematic present: The first consonant of the root was repeated, with -i- as the intervening vowel. The intervening vowel -i- was accented, and the root was in the zero grade. Example:.
 * Thematic present with suffix -sḱé/ó-. The suffix was added to the zero grade of the root, and was accented. Presents of this type often indicated continuous or repeated actions. Example:.
 * Thematic present with suffix -yé/ó-. The suffix was added to the zero grade of the root, and was accented. Presents of this type were typically intransitive and had mediopassive-like meanings. Example:.
 * Thematic present with suffix -ye/o-. The suffix was added to the full grade of the root, and the root was accented. Presents of this type were mostly transitive. Example:.
 * Thematic present with suffix -se/o-. The suffix was added to the full grade of the root, and the root was accented. Example:.
 * Denominative present (secondary) with suffix -yé/ó-. Formed from nouns, very productive. The accent was on the suffix. If formed from a thematic noun, the thematic vowel of the noun remained as -e-, resulting in -eyé/ó-. Likewise, when added to a noun in -eh₂-, the result was -eh₂yé/ó-. Example:.
 * Causative or iterative present (secondary) with suffix -éye/o-. Formed from primary verbs with the verb root in the o-grade. Example:.

Aorist stems
Athematic:
 * Root aorist: The plain verbal root, with no affixes. Identical to the imperfect tense of root presents. Example:.
 * Sigmatic aorist (s-aorist): The root with -s- suffixed. The ablaut and accent variations were like Narten presents. Example:,.

Thematic:
 * Simple thematic aorist: The thematic vowel was added to the root, just like in thematic presents. Thematic aorists were always of the 'tudati' type, so the root was always in the zero grade and the thematic vowel was accented. Example:.
 * Reduplicated thematic aorist: Formed like reduplicated thematic presents, but with -e- as the intervening vowel. Example:.

Perfect stems
All perfect stems were athematic.
 * Root perfect: The plain verbal root, with no affixes. There is only one reconstructible example, all other perfects were reduplicated:.
 * Reduplicated perfect: The first consonant of the root was repeated, with -e- as the intervening vowel. The root was in the o-grade and was accented in the singular, while in the nonsingular the root was in the zero grade and the endings were accented. Example:.

Present stems

 * Thematic:


 * Athematic:

Aorist stems

 * Thematic:


 * Athematic:

Perfect stems

 * Athematic: