already-derived form. 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. This suggests that these moods follow the same constraint, and are derivational in origin. The later Indo-European languages worked around these limitations, but each in their own way. Formation types The following gives a list of the most common verb types reconstructed for (late) PIE. Primary imperfective Root athematic Also called "simple athematic", this formation derived imperfective verbs directly from a root. It can be divided into two subtypes: Normal type: *(é)-ti ~ *(∅)-énti. Alternating between accented e-grade root, and zero-grade root with accent on the endings. Narten type: *(ḗ/é)-ti ~ *(é)-nti. Mostly root accent and alternating lengthened/normal grade, or, according to an alternative view, fixed normal grade throughout. The normal type is the most common by far. Examples: *h₁ésti. Root thematic Also called "simple thematic", it functioned the same as the root athematic verbs. There were also two types: normal type: *(é)-eti ~ *(é)-onti. Accented e-grade root. "tudati" type: *(∅)-éti ~ *(∅)-ónti. Zero-grade root, accent on theme vowel. The "tudati" type is named after the Sanskrit verb that typifies this formation. It is much rarer than the normal type. Examples: *bʰéreti. Reduplicated athematic The root is prefixed with a copy of the initial consonant(s) of the root, separated by a vowel. The accent is fixed on this prefix, but the root grade alternates as in root athematic verbs. The vowel can be either e or i: e-reduplication: *(é)-(e)-ti ~ *(é)-(∅)-nti i-reduplication: *(í)-(e)-ti ~ *(í)-(∅)-nti Examples: *dʰédʰeh₁ti, *stísteh₂ti. Reduplicated thematic *(í)-(∅)-eti ~ *(í)-(∅)-onti. Like the athematic equivalent, but the vowel is always i and the root is always in zero-grade (like in the "tudati" type). Examples: *sísdeti. Nasal infix *(né)-ti ~ *(n)-énti. This peculiar formation consists of an infix -né- ~ -n- that is inserted before final consonant of the zero-grade root, and inflected with athematic inflection. The infix itself ablauts like root athematic verbs. This formation is limited to roots ending in a stop or laryngeal, and containing a non-initial sonorant. This sonorant is always syllabified in the zero-grade, the infix is never syllabic. Examples: *linékʷti, *tl̥néh₂ti. nu-suffix *(∅)-néw-ti ~ *(∅)-nu-énti. Formed with an ablauting athematic suffix *-néw- ~ *-nu- attached to the root. These are sometimes considered to be a special case of the nasal-infix type. Examples: *tn̥néwti. ye-suffix This thematic