Proto-Indo-European verbs

[2][b] For this reason, this system is often thought to have formed not in PIE proper, but at a later stage, after Anatolian and possibly Tocharian had split off.

[2][1][3] The Cowgill-Rix system involves the interplay of six dimensions (number, person, voice, mood, aspect and tense) with the following variables: Further, participles can be considered part of the verbal systems although they are not verbs themselves, and as with other PIE nouns, they can be declined across seven or eight cases, for three genders and three numbers.

PIE roots are morphemes with lexical meanings, which usually consist of a single vowel flanked by one or more consonants arranged to very specific rules.

In the descendant languages, athematic verbs were often extended with a thematic vowel, likely because of the complications resulting from the consonant clusters formed when the mostly consonant-initial endings were added directly onto the mostly consonant-final stems.

In groups such as Germanic and Italic, the athematic verbs had almost gone entirely extinct by the time of written records, while Sanskrit and Ancient Greek preserve them more clearly.

Beekes (1995) uses the t-less forms as the starting point for a radical rethinking of the thematic endings, based primarily on Greek and Lithuanian.

Svensson (2001) suggests *-h₂éy for the second and third dual stative endings, on the basis of evidence from Indo-Iranian, Tocharian, and Gaulish.

The traditional terms are based on the names of the corresponding forms in Ancient Greek (also applied to Sanskrit), and are still commonly encountered.

In Ancient Greek, Armenian and Indo-Iranian, the secondary endings came to be accompanied by a prefixing particle known as the augment, reconstructed as *e- or *h₁e-.

It was traditionally known as perfect, a name which was assigned based upon the Latin tense before the stative nature of the PIE form was fully known.

The stative aspect differed from the eventives by being marked formally with its own personal endings, having a root in the singular in o-grade, but elsewhere in zero-grade, and typically by exhibiting reduplication.

There were a variety of means by which new verbs could be derived from existing verbal roots, as well as from fully formed nominals.

Another notable way of forming imperfective verbs was the nasal infix, which was inserted within the root itself rather than affixed to it.

Thus, there were verbal roots whose default meaning was durative, ongoing, or iterative, and verbs derived from them were generally imperfective in aspect.

For example, the secondary suffix *-éye- derived causative verbs, and retained this purpose and meaning throughout the descendants of PIE.

Conversely, the "s-aorist" formation (retained most notably in Greek) used the suffix -s- to create perfective verbs.

For this root, the imperfective aspect switcher was often reduplication (Ancient Greek hístēmi, Sankskrit tíṣṭhati), but the Germanic languages also show a nasal infix or suffix for this root (Gothic present ik standa vs. preterite ik stōþ), at least by a later period.

The formation of secondary verbs remained part of the derivational system and did not necessarily have completely predictable meanings (compare the remnants of causative constructions in English — to fall vs. to fell, to sit vs. to set, to rise vs. to raise and to rear).

They are distinguished from the primary formations by the fact that they generally are part of the derivational rather than inflectional morphology system in the daughter languages.

Evidence from the Rig Veda (the earliest attestation of Sanskrit) indicates that secondary verbs in PIE were not conjugated in the subjunctive or optative moods.

The following is an example paradigm, based on Ringe (2006), of the verb *leykʷ-, "leave behind" (athematic nasal-infixed present, root aorist, reduplicated perfect).

The following is an example paradigm, based on Ringe (2006), of the verb *bʰer- "carry" in the simple thematic present tense.

The tendency was for various forms to become integrated into a single "paradigm" which combined verbs of different aspects into a coherent whole.

This process proceeded in steps: The gradual tendency in all of the daughter languages was to proceed through the stages just described, creating a single conjugational system that applied to all tenses and aspects and allowing all verbs, including secondary verbs, to be conjugated in all inflectional categories.

In Greek, the difference between the present, aorist, and perfect, when used outside of the indicative (i.e. in the subjunctive, optative, imperative, infinitive, and participles) is almost entirely one of grammatical aspect, not of tense.

A few "tudati"-type athematic verbs survived (*wiganą "to battle", *knudaną "to knead"), but these were usually regularised by the daughter languages.

Some imperfectives with the ye-suffix survived into Proto-Germanic, as did one nasal-infix verb (*standaną "to stand" ~ *stōþ), but these were irregular relics.

For example, the present *pr̥skéti "to ask, to question" was preserved as Germanic *furskōną, which was no longer a simple thematic verb, but had been extended with the class 2 weak suffix -ō-.

A new past tense was also created in the modern languages to replace or complement the aorist and imperfect, using a periphrastic combination of the copula and the so-called "l-participle", originally a deverbal adjective.

The Slavic languages innovated an entirely new aspectual distinction between imperfective and perfective verbs, based on derivational formations.