The ha of nah is changed to dha before a before a jhal (all consonant except semi-vowels and nasals) letter or at the end of a word.,
As नद्धा, नद्धुम्, नद्धव्यम्, उपानत्, परीणत् ॥ The त् of the affixes तृ &c, is changed to ध by 8.2.40; and for the preceding ध is substituted द by 8.4.53. उपानत् is formed by 8.2.39, read with 8.4.56. परीणत् is formed by क्विप् as it belongs to सम्पदादि class, the lengthening is by 6.3.116, and ण-change by 8.4.14. It would have shortened the processes of transformation, had only द been ordained in the sutra, instead of ध; but the ordaining of ध is for the purposes of 8.2.40, by which there should be ध for the participial त &c, in नद्धम्, and that there should not be the change of this Nishtha त into म by 8.2.42. Thus नध् + त = नध् + ध 8.2.40 नद्धम् 8.4.53 But had the substitute been द, we should have नद् + त = नन्नं by 8.2.42.,