Historically, the Arabic letter was used to render either a long [], or a glottal stop []. This led to orthographical confusion, and to introduction of the additional letter hamzatu 'l-qat` . Hamza is not considered a full harf in Arabic orthography: in most cases it appears on a carrier, either a waw, a dotless yā, or an alif. The choice of carrier depends on complicated orthographic rules. Alif is generally the carrier where the only adjacent vowel is fatha. It is the only possible carrier where hamza is the first phoneme of a word. Where alif acts as a carrier for hamza, hamza is added above the alif, or, for initial alif kasra, below it, indicating that the letter so modified does indeed signify a glottal stop, and not a long vowel.
A second type of hamza, hamzatu 'l-wasl, occurs only as the initial phoneme of the definite article and in some related cases. It differs from hamzatu 'l-qat` in that it is elided after a preceding vowel. Again, alif is always the carrier.
The is, as it were, a double alif, expressing both a glottal stop and a long vowel: (final ) , for example in ''
The is actually a dotless , (final ) (ISO 233 ) pronounced .
