न वा-इति विभाषा

This sutra defines the word विभाषा. We had already had occasion to use this word in sutras 1.1.28 and 1.1.32. Where there is a prohibition as well as an alternative course left open, it is called option or vibhasha. The commentators mention three kinds of vibhasha:- prapta-vibhasha., aprapta-vibhasha and praptaprapta-vibhasha. The first occurs where there is a general rule already given, and then follows the optional rule; the second belongs to that class where there is no such general rule, but there is an optional rule, the third is intermediate between the two.

Thus the root श्वि, 'to swell,' by virtue of the rule विभाषा श्वे 5.1.30, forms its perfect tense, either by samprasarana, or in the ordinary way. Thus the third person singular is either शुशाव or शिश्वाय.,