[5] This insight has led to the development of modern theories regarding the relation of PIE accent, ablaut and the resulting ablaut classes: all roots, suffixes and inflectional endings (desinences) can be inherently "accented" or not, and the surfacing stress (i.e. the accent of the PIE word) falls on only one syllable, depending on the interplay of underlying accentuation of the combining morphemes.
[6] Narten-type ablaut with a lengthened-grade singular and a full grade elsewhere is speculated to have been the original form of the Proto-Indo-European s-aorist, which had the root in the lengthened e-grade in Indo-Iranian, Italic and Slavic, but in the full-grade in Greek and the Indo-Iranian middle.
[7] Proto-Indo-European long-vowel preterites with */ē/ in the root are according to some originally imperfects of Narten presents, which explains the lengthened grade.
de Vaan (2004) analyzes the evidence collected by Schindler and Narten on acrostatic inflection in Avestan and PIE and concludes that "the concept of 'Narten' roots can be abandoned altogether.".
[9] On the other hand, Lexikon der indogermanischen Verben classifies Narten roots under the type (1b) "acrodynamic present", reconstructing in total 52 PIE roots belonging to this inflectional class, of which 32 are marked as "certain" and 20 as "uncertain".