The augment is a prefix used in certain Indo-European languages (Indo-Iranian, Greek, Armenian and Phrygian) to indicate past time. The augment is of rather late origin in Proto-Indo-European, and in the oldest daughter languages such as Vedic Sanskrit and early Greek, it is used optionally. The same verb forms when used without the augment carry an injunctive sense.
The augment originally appears to have been a separate word, with the potential meaning of 'there, then', which in time got fused to the verb. The augment is *é- in PIE (é- in Greek, á- in Sanskrit) and always bears the accent.
In Ancient Greek, the verb λέγω légo "I say" has the aorist ἔλεξα élexa "I said." The initial ε e is the augment. When it comes before a consonant, it is called the "syllabic augment" because it adds a syllable. Sometimes the syllabic augment appears before a vowel because the initial consonant of the verbal root (usually digamma) was lost:
When the augment is added before a vowel, the augment and the vowel are contracted and the vowel becomes long: ἀκούω akoúō "I hear", ἤκουσα ḗkousa "I heard". It is sometimes called the "temporal augment" because it increases the time needed to pronounce the vowel.
Unaccented syllabic augment disappeared during the Byzantine period as a result of the loss of unstressed initial syllables. However, accented syllabic augments have remained in place. So Ancient ἔλυσα, ἐλύσαμεν (élūsa, elū́samen) "I loosened, we loosened" corresponds to Modern έλυσα, λύσαμε (élisa, lísame). The temporal augment has not survived in the vernacular, which leaves the initial vowel unaltered: Ancient ἀγαπῶ, ἠγάπησα (agapô, ēgápēsa) "I love, I loved"; Modern αγαπώ, αγάπησα (agapó, agápisa).
The augment is used in Sanskrit to form the imperfect, aorist, pluperfect[a] and conditional. When the verb has a prefix, the augment always sits between the prefix and the root. The following examples of verb forms in the third-person singular illustrate the phenomenon:
In J. R. R. Tolkien's Quenya, the repetition of the first vowel before the perfect (for instance utúlië, perfect tense of túlë, "come") is reminiscent of the Indo-European augment in both form and function, and is referred to by the same name in Tolkien's grammar of the language.