Tamil alphabets

[John Oliver Perry]

As an ignoramus in such matters, I am wondering why it is assumed (it seems
from recent exchanges by N. Ganesan, et al.) that alphabets are constructed
logically or will evolve logically over eons of varied use?

        I am aware that the so-called Roman alphabet uses the letter "c" (in
various languages) to stand for a variety of sounds which have not been
distinguished elsewhere in the alphabet, despite the confusion over how to
read-and-sound that letter.  Is the Brohmi-Devanagari alphabet entirely
logical?  So why should the Tamil be?   Did the equivalent of the Tamil
Academy arrange it perfectly at an early period so as to take care of all
(then used) sounds separately?

    Since I approach this question without any knowledge of the history of
the Tamil language, but also, as I am here suggesting, without any
assumptions about it, I may be answered simply about the assumption of
logicality-- or else off-channel.  ATB  JOP