in consonantal writing, the consonants (w, j, and in some writing systems the laryngeals ’ or h) used to indicate the presence of vowels (primarily long vowels) in order to ensure the correct reading of a text which, if written without the indication of vowel sounds, would often be ambiguous.
The matres lectionis are found in Ugaritic, Moabite, and Phoenician writing, but are used widely only in the writing systems of Hebrew, Aramaic, Syrian, and Arabic. The letter j indicates the presence of ī, ē (and even ā); w indicates ū, ō the laryngeal’ and final h—the presence of ă and other long vowels. In later alphabets (Mandaean, Avestan), the matres lectionis regularly denote all vowels; that is, they are transformed into vowel letters. In the Greek language, the letters used to indicate vowels originated from the matres lectionis; for example, I from j; v from w; A from ’; E from h; O from ‘; H (ē) from h. The vowels of Latin, Cyrillic, and many other alphabets can be traced to the matres lectionis.