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In the spelling of Hebrew and some other Semitic languages, matres lectionis (Latin "mothers of reading", singular form: mater lectionis, Hebrew: אֵם קְרִיאָה mother of reading), refers to the use of certain consonants to indicate a vowel. The letters that do this in Hebrew are א aleph, ה he, ו waw (or vav) and י yod (or yud). The yod and waw in particular are more often vowels than they are consonants. In Arabic, the matres lectionis (though they are much less often referred to thus) are alif ا, waw و, and ya' ي.
Because the scripts used to write some Semitic languages lack vowel letters, unambiguous reading of a text might be difficult. Therefore, to indicate vowels (mostly long), consonant letters are used. For example, in the Hebrew construct-state form bēt, meaning "the house of", the middle letter "י" in the spelling בית acts as a vowel, whereas in the corresponding absolute-state form bayit ("house"), which is spelled the same, the same letter represents a genuine consonant. Matres lectionis are found in Ugaritic, Moabite, South Arabian and the Phoenician alphabets, but are widely used only in Hebrew, Aramaic, Syriac and Arabic.
An early method for indicating long vowels using the Hebrew alphabet was to write the consonant letters yod י, waw ו, he ה,and aleph א. Originally א and ה were put only at the end of words, while י and ו were used mainly to write the original diphthongs /aw/ and /aj/, as well as original vowel+[y]+vowel sequences (which sometimes simplified to plain long vowels). So for example, ṣādĕqā - she is righteous; ṣidqī - my righteousness; ṣidqō - his righteousness. Gradually, as this was found to be insufficient for differentiating between similar nouns, they were inserted in medial positions, e.g., ṣaddīq - righteous; ṣādōq – Zadok.
Where words can be written either with or without matres lectionis, spellings that include these letters are called malē (Hebrew) or plene (Latin), meaning "full", while spellings without them are called ḥaser or defective. In some verb forms, matres lectionis are almost always used. In the 800's, it was decided that the system of matres lectionis did not suffice to indicate the vowels precisely enough, so a supplemental vowel pointing systems (niqqud) (diacritic symbols indicating vowel pronunciation and other important phonological features not written by the traditional basic consonantal orthography) joined matres lectionis as part of the Hebrew writing system.
In some words in Hebrew there is a choice of whether to use a mater lectionis or not, and in modern printed texts matres lectionis are sometimes used even for short vowels, which is considered to be grammatically incorrect, though instances are found as far back as Talmudic times. Such texts from Israel were noticeably more inclined to malē spellings than texts from Babylonia: this may reflect the influence of Greek, which had full alphabetic spelling. Similarly in the Middle Ages Ashkenazim tended to use malē spellings under the influence of European languages, while Sephardim tended to use ḥaser spellings under the influence of Arabic.
In Arabic there is no such choice, and the almost invariable rule is that a long vowel is written with a mater lectionis and a short vowel with a diacritic symbol, although the Othmani orthography, the one in which the Qur'an is traditionally written and printed, has some differences which are not always consistent. Also, under influence from orthography of European languages, transliterating of borrowed words into Arabic is usually done using vowels in place of diacritics, even when the latter is more suitable, and even when transliterating words from another Semitic language, such as Hebrew, a phenomenon augmented by the neglect of diacritics in most printed forms since the beginning of mechanical printing.
Informal, de facto orthographies of spoken varieties of Arabic also use ha to indicate a shorter version of alif, a usage augmented by the ambiguity of the use of ha and taa marbuta in formal Arabic orthography, and also a formal orthography in some languages that use Arabic script, such as Kurdish orthography
Syriac-Aramaic vowels are classified into three groups: the Alap (ܐ), the waw (ܘ), and the yod (ܝ). 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 most frequent ones are the yod and the waw while the alap is mostly restricted to some transliterated words.
Usage in Hebrew 
Most commonly, yod י indicates i or e, while waw ו indicates o or u. Aleph א was not systematically developed as a mater lectionis in Hebrew (as it was in Aramaic and Arabic), but it is occasionally used to indicate an a vowel. (However, a silent aleph — indicating an original glottal stop consonant sound which has become silent in Hebrew pronunciation — can occur after almost any vowel.) At the end of a word, He ה can also be used to indicate that a vowel a should be pronounced.
Symbol Name Vowel formation Vowel quality Example Biblical Modern Hebrew Transliteration א Alef ê, ệ, ậ, â, ô mostly ā פארן Paran ה He ê, ệ, ậ, â, ô mostly ā or e לאה Leah משה Moshe ו Waw Vav ô, û ō or ū יואל Yo'el ברוך Baruch י Yod Yud î, ê, ệ ī, ē or ǣ דויד David
Origins and development 
Historically, the practice of using matres lectionis seems to have originated when /aj/ and /aw/ diphthongs (written using the yod י and waw ו consonant letters respectively) monophthongized to simple long vowels /eː/ and /oː/. This epiphenomenal association between consonant letters and vowel sounds was then seized upon and used in words without historic diphthongs.
In general terms, it is observable that early Phoenician texts have very few matres lectionis, and that during most of the 1st millennium BCE, Hebrew and Aramaic were quicker to develop matres lectionis than Phoenician. However, in its latest period of development in North Africa (referred to as "Punic"), the Phoenician language developed a very full use of matres lectionis (including the use of the letter `Ayin ע, also used for this purpose much later in Yiddish orthography).
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. This was probably inspired by the phonological change of the third-person singular possessive suffix from /ahuː/ > /aw/ > /oː/ in most environments. However, in later periods of Hebrew the orthography was changed so that word-final ō was no longer written with the letter He ה (except in a few archaically-spelled proper names, such as Solomon שלמה and Shiloh שלה). The difference between the spelling of the third-person singular possessive suffix (as attached to singular nouns) with He ה in early Hebrew vs. with waw ו in later Hebrew has become an issue in the authentication of the Jehoash Inscription.
According to Sass (5), already in the Middle Kingdom there were some cases of matres lectionis, i.e. consonant graphemes which were used to transcribe vowels in foreign words, namely in Punic (Jensen 290, Naveh 62), Aramaic, and Hebrew (he, waw, yod; sometimes even aleph; Naveh 62). Naveh (ibid.) notes that the earliest Aramaic and Hebrew documents already used matres lectionis. Some scholars argue that therefore the Greeks must have borrowed their alphabet from the Arameans. But the practice has older roots: the Semitic cuneiform alphabet of Ugarit (13th century BC) already has matres lectionis (Naveh 138).
Influence on other languages 
Later, in some adaptations of the Arabic alphabet (such those used for Persian and Urdu) and of the Hebrew alphabet (such as those used for the Yiddish and Ladino languages), matres lectionis were generally used for all or most vowels, thus in effect becoming vowel letters: see Yiddish orthography. This tendency was taken to its logical conclusion in fully alphabetic scripts such as the Greek, Roman and Cyrillic alphabets. Many of the vowel letters in these languages historically go back to matres lectionis in the Phoenician script: for example, the letter <i> was originally derived from the consonant letter yod. Similarly the vowel letters in Avestan are adapted from matres lectionis in the version of the Aramaic script used for Pahlavi.
See also 
- Gesenius' Hebrew Grammar, §7
- Garr, W. Randall. 1985. Dialect Geography of Syria-Palestine, 1000-586 B.C.E. Philadelphia: University of Pennsylvania Press.
- Jensen, Hans. 1970. Sign Symbol and Script. London: George Allen and Unwin Ltd. Transl. of Die Schrift in Vergangenheit und Gegenwart. VEB Deutscher Verlag der Wissenschaften. 1958, as revised by the author.
- Naveh, Joseph. 1979. Die Entstehung des Alphabets. Transl. of Origins of the Alphabet. Zürich und Köln. Benziger.
- Sass, Benjamin. 1991. Studia Alphabetica. On the origin and early history of the Northwest Semitic, South Semitic and Greek alphabets. CH-Freiburg: Universitätsverlag Freiburg Schweiz. Göttingen: Vandenhoeck & Ruprecht.