The preservation of certain linguistic forms current in the Old Irish period may provide reason to assume that an Old Irish original directly or indirectly underlies the transmitted text or texts. Phonology Consonants The consonant inventory of Old Irish is shown in the chart below. The complexity of Old Irish phonology is from a four-way split of phonemes inherited from Primitive Irish, with both a fortis–lenis and a "broad–slender" (velarised vs. palatalised) distinction arising from historical changes. The sounds are the broad lenis equivalents of broad fortis ; likewise for the slender (palatalised) equivalents. (However, most sounds actually derive historically from .) {| class="wikitable" style="text-align: center;" ! colspan="2" | ! Labial ! Dental ! Alveolar ! Velar ! Glottal |- ! rowspan="2" | Nasal ! | | colspan="2" | | | |- ! | | colspan="2" | | | |- ! rowspan="2" | Plosive ! | | colspan="2" | | | |- ! | | colspan="2" | | | |- ! rowspan="2" | Fricative ! | | | | | |- ! | | | | | |- ! rowspan="2" | Nasalized fricative ! | | | | | |- ! | | | | | |- ! rowspan="2" | Approximant ! | | colspan="2" | | | |- ! | | colspan="2" | | | |- ! rowspan="2" | Lateral ! | | colspan="2"| | | |- ! | | colspan="2" | | | |} Some details of Old Irish phonetics are not known. may have been pronounced or , as in Modern Irish. may have been the same sound as or . The precise articulation of the fortis sonorants is unknown, but they were probably longer, tenser and generally more strongly articulated than their lenis counterparts , as in the Modern Irish and Scottish dialects that still possess a four-way distinction in the coronal nasals and laterals. and may have been pronounced and respectively. The difference between and may have been that the former were trills while the latter were flaps. and were derived from an original fortis–lenis pair. Vowels Old Irish had distinctive vowel length in both monophthongs and diphthongs. Short diphthongs were monomoraic, taking up the same amount of time as short vowels, while long diphthongs were bimoraic, the same as long vowels. (This is much like the situation in Old English but different from Ancient Greek whose shorter and longer diphthongs were bimoraic and trimoraic,