Schwa Indogermanicum
The term "schwa" is also used for vowels of uncertain quality (rather than neutral sound) in the reconstructed Proto-Indo-European language. It was observed that, while for the most part a in Latin and Ancient Greek corresponds to a in Sanskrit, there are instances where Sanskrit has i while Latin and Greek have a, such as pitar (Sanskrit) vs pater (Latin and Ancient Greek). This postulated "schwa indogermanicum" evolved into the theory of the so-called laryngeals. Most scholars of Proto-Indo-European would now postulate three different phonemes rather than a single indistinct schwa. Some scholars postulate yet more, to explain further problems in the Proto-Indo-European vowel system. Most reconstructions of *-ə- in older literature would correspond to *-h2- in contemporary notation.
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