different names popularly. Six letters () do not have a distinct medial form and have to be written with their final form without being connected to the next letter. Their initial form matches the isolated form. The following letter is written in its initial form, or isolated form if it is the final letter in the word. The letter originated in the Phoenician alphabet as a consonant-sign indicating a glottal stop. Today it has lost its function as a consonant, and, together with and , is a mater lectionis, a consonant sign standing in for a long vowel (see below), or as support for certain diacritics ( and ). Arabic currently uses a diacritic sign, , called , to denote the glottal stop , written alone or with a carrier: alone: with a carrier: (above or under an ), (above a ), (above a dotless or ). In academic work, the () is transliterated with the modifier letter right half ring (ʾ), while the modifier letter left half ring (ʿ) transliterates the letter (), which represents a different sound, not found in English. The has a single form, since it is never linked to a preceding or following letter. However, it is sometimes combined with a , , or , and in that case the carrier behaves like an ordinary , , or . Variations Alif Modified letters The following are not individual letters, but rather different contextual variants of some of the Arabic letters. Ligatures The use of ligature in Arabic is common. There is one compulsory ligature, that for ل + ا, which exists in two forms. All other ligatures, of which there are many, are optional. A more complex ligature that combines as many as seven distinct components is commonly used to represent the word . The only ligature within the primary range of Arabic script in Unicode (U+06xx) is + . This is the only one compulsory for fonts and word-processing. Other ranges are for compatibility to older standards and contain other ligatures, which are optional. + Note: Unicode also has in its Presentation Form B FExx range a code for this ligature. If your browser and font are configured correctly for Arabic, the ligature displayed above should be identical to this one, U+FEFB ARABIC LIGATURE LAM WITH ALEF ISOLATED FORM: U+0640 ARABIC TATWEEL + + Note: Unicode also has in its Presentation Form B U+FExx