ó, and it is unclear whether existed as a separate sound any time in the Old Irish period. 3 existed only in early archaic Old Irish (700 or earlier); afterwards it merged into . Neither sound occurred before another consonant, and both sounds became ó in later Old Irish (often ú or u before another vowel). The late ó does not develop into úa, suggesting that áu > ó postdated ó > úa. Later Old Irish had the following inventory of long vowels: {| class="wikitable" style="text-align: center;" ! ! colspan="2" | Monophthongs ! colspan="2" | Diphthongs |- ! Close | | | | |- ! Mid | | | | 1 |- ! Open | colspan="2" | | colspan="2" | |} 1Early Old Irish and merged in later Old Irish. It is unclear what the resulting sound was, as scribes continued to use both aí and oí to indicate the merged sound. The choice of in the table above is somewhat arbitrary. The distribution of short vowels in unstressed syllables is a little complicated. All short vowels may appear in absolutely final position (at the very end of a word) after both broad and slender consonants. The front vowels and are often spelled ae and ai after broad consonants, which might indicate a retracted pronunciation here, perhaps something like and . All ten possibilities are shown in the following examples: {| class="wikitable" |- ! Old Irish ! Pronunciation ! English ! Annotations |- | | | kill | 1 sg. subj. |- | | | leave | 1 sg. subj. |- | | () | kill | 2 sg. subj. |- | | | leave | 2 sg. subj. |- | | (?) | kill | 2 sg. indic. |- | | | leave | 2 sg. indic. |- | | | eye | gen. |- | | | door | gen. |- | | | kill | 1 sg. indic. |- | | | leave | 1 sg. indic. |} The distribution of short vowels in unstressed syllables, other than when absolutely final, was quite restricted. It is usually thought that there were only two allowed phonemes: (written a, ai, e or i depending on the quality of surrounding consonants) and (written u or o). The phoneme tended to occur when the following syllable contained an *ū in Proto-Celtic (for example, "law" (dat.) < PC *dligedū), or after a