[3] Because the scripts used to write some Semitic languages lack vowel letters, unambiguous reading of a text might be difficult.
Matres lectionis are extensively employed only in Hebrew, Aramaic, Syriac and Arabic, but the phenomenon is also found in the Ugaritic, Moabite, South Arabian and Phoenician alphabets.
Historically, the practice of using matres lectionis seems to have originated when /aj/ and /aw/ diphthongs, written with the yod י and the waw ו consonant letters respectively, monophthongized to simple long vowels /eː/ and /oː/.
In pre-exilic Hebrew, there was a significant development of the use of the letter he ה to indicate word final vowels other than ī and ū.
However, in later periods of Hebrew, the orthography was changed so word-final ō was no longer written with ה, except in a few archaically-spelled proper names, such as Solomon שלמה and Shiloh שלה.
However, the practice has older roots, as the Semitic cuneiform alphabet of Ugarit (13th century BC) already had matres lectionis (Naveh 138).
Gradually, as it was found to be insufficient for differentiating between similar nouns, י and ו were also inserted to mark some long vowels of non-diphthongal origin.
The name given to the three matres lectionis by traditional Arabic grammar is ḥurūf al-līn wa-l-madd (حروف اللين والمدّ, 'consonants of softness and lengthening'), or ḥurūf al-ʿilla (حروف العلّة, 'causal consonants' or 'consonants of infirmity', because as in Greek grammar, words with 'accidents' were deemed to be afflicted, ill, in opposition to 'healthy' words without accidents).
The mater lectionis was developed as early as the 6th century to represent long vowels, which were earlier denoted by a dot under the line.
The eighth letter corresponds to the Semitic heth, and is called eh; it is pronounced as a long i-vowel but is used only as a suffix for the third person singular.