the length, as short (kuril) and long(nedil). The short vowels are pronounced for a duration 1 unit, while the long vowels take two units. Based on the duration of the sound, the vowels form 5 pairs. The other two vowels ஐ(ai) and ஔ(au) are diphthongs formed by joining the letters அ(a)+இ(i) and அ(a)+உ(u). Since these two are a combination two short letters, their pronunciation takes 2 units of time, that is they fall under nedil category. ஐ(ai) and ஔ(au) can also be spelt அய் and அவ். This form is known as eḻuttuppōli and is generally not recommended. The consonants are categorised into three groups, (hard), (soft) and (medium), based on the nature of the sound. From the 30 prime letters, the dependent letters are formed. Dependent Letters Tamil grammar defines 10 categories of Dependent letters. Alphasyllabic letters Aidam Elongated vowel Elongated consonant Shortened u Shortened i Shortened ai Shortened au Shortened m Shortened Aidam The alphasyllabic letters – 216 in total – are formed by combining the consonants and the vowels. The duration of the sound is that of the vowel attached to the consonant (or the inherent vowel, in case of the pure consonants). For example, the table below shows the formation of க் based letters. Aidam is also known as (stand alone). The aidam is always preceded by a single short letter ( ) and followed by a hard alphasyllabic letter ( ). It takes half unit time for pronunciation. () and () are formed by elongating the duration of pronunciation of a letter to satisfy certain grammatical rules while composing poetry. In Uyiralapetai, the intrinsic vowel of the letter that is elongated is written next to it, to indicate that the letter now is pronounced for 3 units of time. In Kutriyalukaram, the duration of the short 'u' letters of vallinam category (கு, சு, டு, து, பு, று) is reduced to half units, when the letter is found at the end of the word, preceded by multiple letters or a single nedil(long) letter. If a word with kutriyalikaram is followed by a word with 'ய'(ya) as the first letter, the u sound is corrupted to i sound and takes a half unit of time for pronunciation. In Aikarakurukkam and Aukarakurukkam, the duration of the letters ஐ and ஔ are reduced to 1 1/2 units if they are the first letters of the word. If situated elsewhere it