^ abcdOnly when preceded by a nasal consonant or when not preceded by a stop consonant. Never word-initial.
^This letter does not belong to Tamil script, but is widely accepted as an ad-hoc from Grantha script ( See Usage of other lingual consonants in Tamil script). This sound may be replaced by ச (as in s) in pure Tamil, which is not an accurate phonetic representation.
^Only when preceded by a nasal consonant or not preceded by a stop consonant
^(only as an intervocalic in colloquial speech;not when it appears as the first letter of a word,
^As a first letter of a word or preceded by stop consonants
^As intervocalic and not preceded by stop consonant or permitted soft consonant
^As a first letter of a word or when preceded by stop consonants
Bibliography
Keane, Elinor (2004), "Tamil", Journal of the International Phonetic Association34 (1): 111–116, doi:10.1017/S0025100304001549