 Although Kātyāyana and Patañjali argue that the notion of change or transformation of parts of words was contradictory to the doctrine of nityatva (“permanence”) of language, they were not averse to the notion of substitution. The notion of substitution was understood as a substitution, not of a part of a word by another part, but of a whole word by another word, and this especially as a conceptual rather than an ontological replacement. Thus, in going from “bhavati” to “bhavatu”, Pāṇini prescribes the change of “i” of “ti” to “u” (cf. P.3.4.86: “er uḥ”). Thus, “i” changes to “u”, leading to the change of “ti” to “tu”, and this consequently leads to the change of “bhavati” to “bhavatu”. For Kātyāyana and Patañjali, the above atomistic and transformational understanding of Pāṇini’s procedure goes contrary to the doctrine of nityatva (“permanence”) of words. Therefore, they suggest that it is actually the substitution of the whole word “bhavati” by another whole word “bhavatu”, each of these two words being eternal in its own right. Additionally they assert that this is merely a notional change and not an ontological change, i.e., a certain item is found to occur, where one expected something else to occur. There is no change of an item x into an item y, nor does one remove the item x and place y in its place (Vārttikas 12 and 14 on P. 1.1.56). This discussion seems to imply a sort of unitary character to the words, whether notional or otherwise, and this eventually leads to a movement toward a kind of akhaṇḍa-pada-vāda (“the doctrine of partless words”) in the Vākyapadīya of Bhartṛhari. While one must admit that the seeds for such a conception may be traced in these discussions in the Mahābhāṣya, Patañjali is actually not arguing so much against words having parts, as against the notion of change or transformation (Mahābhāṣya on P. 1.2.20, I, p. 75).