Here are some passages from” Tholkappiyam-in English with critical studies” (p.273-275) by Dr.S.Ilakkuvanar, which explain the uniqueness of Tamil alphabet.
“Though there are twenty eight consonant sounds in Tamil, Tholkappiyar has given only eighteen sounds. Why has he failed to recognize ten more sounds? No grammar of Tamil language cared to recognize them till now. They are not represented by separate characters in the Tamil alphabet. So some letters have to represent more than one sound. The system of representing more than one sound by a single character is considered defective by some scholars. Some have ventured to invent new characters for representing more sounds such as j, sh, h, f and g, which are found in the words of other languages without understanding the genius of the Tamil language and without knowing the dictum of Tholkasppiyar about the use of words.(verse 401 of sol.)”
“Dr.Caldwell alone understood this peculiar system of representing more than one sound by a single letter and termed it as the law of convertibility of Surds and sonants remarking ‘that the Tamilian rule which requires the same consonant to be pronounced as k in one position and g in another, as t, th, p in one position and as d, dh, b in another is not a mere dialectic peculiarity, the gradual result of circumstances or a modern refinement invented by grammarians; but is essentially inherent in the language and has been a characteristic principle of it from the beginning.’(Comparative grammar of Dravidian Languages-Page-139)”
“According to Whitney, any language that has mute closures (k,c,t,p)will have also the other related sonants and nasals; thus the presence of a ‘p’ in the alphabet implies also that of a b and an m and so on. There fore it is to be inferred that even the ancient Tamil of Tholkappiyar-period possessed sonants.It cannot be considered as a defect of the Tamil language,for having not separate characters to represent them in the alphabet system.Vendryes says”that the number of phonemes in a language cannot of course be calculated by the number of signs in its alphabet. Language generally has more sounds than signs. This is the case in French, Italian, English and German.’
courtesy: Maraimalai
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TAMIL RESEARCH TOWARDS TRUTH 