vowels that characterize their endings), limited the archaic Irish endings of the singular genitive to , , and . The first ending, , is found in words equivalent to the Proto-Celtic o-stem nouns. This category was also registered in the dative as -u, with a possible occurrence of the use of the nominative, also in -u. , in turn, is equivalent to Proto-Celtic i-stems and u-stems, while corresponds to ā-stems. The exact function of remains unclear. Furthermore, according to Damian Mcmanus, Proto-Celtic nasal, dental, and velar stems also correspond to the Primitive Irish genitive, attested in names such as , , and . Phonology It is possible, through comparative study, to reconstruct a phonemic inventory for the properly attested stages of the language using comparative linguistics and the names used in the scholastic tradition for each letter of the ogham alphabet, recorded in the Latin alphabet in later manuscripts. Vowels There is a certain amount of obscurity in the vowel inventory of Primitive Irish: while the letters Ailm, Onn and Úr are recognized by modern scholars as , and , there is some difficulty in reconstructing the values of Edad and Idad. They are poorly attested, probably an artificial pair, just like peorð and cweorð of the futhorc, but probably have the respective pronunciations of and . There were also two diphthongs, written as and . In later stages of the language, scholastic oghamist traditions incorporated five new letters for vowels, called forfeda, corresponding to digraphs of the orthodox spelling, but these no longer corresponded to Primitive Irish sounds. Consonants The consonant inventory of Primitive Irish is reconstructed by celtologist Damian McManus as follows: The letters cért, gétal and straif, respectively transliterated as , (or ) and , were known by the ancient scholastic oghamists as foilceasta (questions) due to the obsolescence of their original pronunciations: the first two, and , had merged with plain velars in Old Irish, and the third, probably , merged with . However, evidence of the original distinction between Straif and Sail was still present into the Old Irish period, as the séimhiú (lenition) of produced for lexemes with original Straif but for lexemes with original Sail. The letter Úath or hÚath, transliterated as , although not counted among the foilceasta, also presented particular difficulties due to apparently being a silent letter. It was probably pronounced as in an early stage of Primitive Irish, disappearing