> In 1878, a student called Ferdinand de Saussure proposed that PIE had only one vowel sound "e", and that all other vowel sounds in PIE languages came that sin

> In 1878, a student called Ferdinand de Saussure proposed that PIE had only one vowel sound "e", and that all other vowel sounds in PIE languages came that single sound. That's not in perfect agreement with wiki: > The beginnings of the [laryngeal] theory were proposed by Ferdinand de Saussure in 1879, in an article chiefly demonstrating that a and o were separate phonemes in PIE. And: > In the course of his analysis, Saussure proposed that what had then been reconstructed as long vowels ā and ō, alternating with ǝ, was an ordinary type of PIE ablaut. That is, it was an alternation between e grade and zero grade like in "regular" ablaut (further explanations below), but followed by a previously unidentified element. This element accounted for both the changed vowel colour and the lengthening (short e becoming long ā or ō).