sutras and shastras

[Shyam Ranganathan]

Dear list members

I have a question that will no doubt expose my historical naiveté to the
historians on the list:

I've always thought that the switch from sutra format to shastra format in
Indian philosophical literature had something to do with the technological or
cultural innovation of writing: sutras are preferred when one cannot write
because they are short and easily memorized. Shastras are preferred when one can
commit thoughts to an inscription because of the reduction of ambiguity afforded
by increased text size. Thus, at some point it seems that philosophers in all
schools generally stopped writing sutras and started writing treatise and
commentaries (that is, unless they wanted to secure some type of ancient origin
for their text, as in the case of the Mahayana Sutras). 

Is this account correct? Is there anything like a technological or cultural
innovation that tigers the move from sutra to shastra format? Or is it simply
the case that Indians always composed treatises, but the older ones haven't
survived. 

Thanks in advance

Shyam Ranganathan