After the verb vad , the ātmanepada is used optionally, when the sense is that of 'contradicting with each other'.,
As विप्रवदन्ते or न्ति वैद्याः (the doctors are at variance). The words vyaktavacham (articulate utterance) and samuchcharana (speaking together) are understood in this sutra also.
No option is allowed when the sense is not that of contradiction or wrangling as, संप्रवदन्ते ब्राह्मणाः, 'the Brahmanas are speaking together.'
The phrase 'articulate utterance' is necessary in this also. Because as विप्रवदन्ति शकुनयः 'the kites are quarrelling,' the verb is in the Parasmaipada.
The wrangling must be by talking at one and the same time, otherwise this rule will not apply. As क्रमेण वैद्या वैद्येन सह विप्रवदन्ति, 'the doctors contradict by turn another doctor.',