A complete list of these exceptions is available here. There are some non-standard consonant-vowel combinations in Tamil that don’t follow these rules.When ஔ au is added to a consonant, the diacritic mark for e is placed at the beginning of the consonant and another diacritic mark is placed at the end, as in கௌ kau.
When ஏ ee is added to a consonant, a diacritic mark representing it is placed in front of the consonant, as in கே kee.When எ e is added to a consonant, a modified form is placed in front of the consonant, as in கெ ke.When ஊ uu is added to a consonant, a diacritic mark representing it is added to the end of the consonant, as in கூ kuu.When உ u is added to a consonant, a diacritic mark representing it is added to the bottom of the consonant, as in கு ku.When ஈ ii is added to a consonant, a diacritic mark representing it is added to the top of the consonant, as in கீ kii.When இ i is added to a consonant, a diacritic mark representing it is added to the end of the consonant, as in கி ki.When ஆ aa is added to a consonant, a diacritic mark representing it is added to the end of the consonant, as in கா kaa.
Similar to many other South Asian scripts, Tamil consonants carry the inherent அ a sound, so அ a does not change when added to a consonant.(Long vowels are held about twice as long as short vowels.) In some cases, diacritic marks are added to the end of the consonants to represent vowels, but in others, marks are added to other locations. They alter their form depending on whether they are paired with a consonant and whether they are short or long vowels. The Tamil script has 12 vowels, which are written as independent letters when they appear at the beginning of a syllable.