छन्दस्युभयथा

In the छन्दस् (Vedas) this distinction of सार्वधातुक and आर्द्धधातुक is not always maintained and the affixes are promiscuously used.
In the Vedas, there is no hard and fast rule about sarvadhatuka and ardhadhatuka affixes. Sometimes the तिङ् and शित् are treated as if they were ardhadhatuka. Thus वर्धन्तु त्वा सुष्टुतयः । Here the affixes of the लोट् are treated as ardhadhatuka and consequently there is the elision of the णिच् by rule 6.4.51; the proper form of this word would be वर्धयन्तु । Sometimes ardhadhatuka affixes are treated like sarvadhatuka affixes; as विशृण्विरे; here the affixes of the लिट् are treated as sarvadhatuka and so there is the Vikarana श्नु and the उ is changed into व । Thus, वि + शृ + श्नु + इरे = वि + शृ + नु + इरे 3.1.74 = वि + शृ + न्व् + इरे 6.4.87 = विशृण्विरे । Similarly, सुन्विरे । The लिङ् is sometimes treated in the Vedas both as sarvadhatuka and ardhadhatuka at one and the same time; as उपस्थेयाम् शरणं बृहन्तम् । Here, by treating the affix as sarvadhatuka, there is elision of स in the लिङ् 7.2.79 and by treating it again as ardhadhatuka, the आ of स्था is changed into ए । So also in स्वस्ति the affix is treated as sarvadhatuka_ and there is no substitution of भू for अस् as required by 2.4.52.