ईद्-ऊतौ च सप्तम्य्-अर्थे

This sūtra finds its scope in the Vedic literature generally. There is a sūtra 7.1.39 which declares that \in the Vedic Sanskrit, the case-affixes sup are often replaced either by सु (I.S.), or are altogether elided, or they are changed into a letter homogeneous with the prior letter, or आ, or आत्, or शे, or या, or डा, or ड्या, or याच्, or आल् takes their place.\ Let us take the example where a case-affix is changed into a letter homogeneous with the prior. Thus the case-affix of the seventh case is ङि (इ). In forming the 7.S. of तनू \body,\ we have तनू+इ. The इ will be changed into a homogeneous letter with ऊ and we have तनू+ऊ=तनू \in the body,\ as, अध्यस्यां मामकीतनू (for मामक्यां तन्वाम्). This is the Vedic form, the secular form being तन्वाम्. Similarly गौरी+इ = गौरी \on the Gauri,\ as सोमो गौरी अधिश्रितः (Rig Veda IX.12.3). It is in such cases, therefore, that the long ī and ū are used in the sense of locative, and are pragrihya.

It is only long ī and ū which are pragrihya, and not any other vowel, though used in the sense of locative. Thus by the same aphorism (VII.I.39) ḍå (â) may be employed to denote the seventh case-affix. Thus अग्नि+ङि = अग्नि+डा = अग्ना \in the fire,\ as, प्रियः सूर्ये प्रियो अग्ना भवाति य इन्द्राय सुतसोमो ददाशत् (Rig Veda V.37.5). Here अग्ना though in the locative case, its final is not pragrihya. Therefore अग्ना+इति = अग्नेति.

The ई and ऊ must be of the 7th case. Therefore मति+टा (3rd S.) = मति+इ (letter homogeneous with the prior) = मती 'with wisdom'. Here ī is in the sense of the instrumental case and is not pragrihya. Thus मती+इति = मतीति.

The word अर्य is used in the aphorism, in order to exclude the application of this rule to cases like the following. Thus in forming the compound of वाप्याम् \in the well\ and अश्व \horse\, the case-affix is elided, and we get वापी + अश्व. Here, no doubt, the word वापी is in the locative case, though the case-affix is elided; but we cannot say that the long ई of vâpî has the sense of the locative. Here, therefore, we shall have sandhi; as, वाप्यश्वः \the horse near the well.\ In other words, the present aphorism is not to apply to the final ई or ऊ of words standing as the prior member of a compound term (pûrva-pada); for words like वापी &c., in the above example, can never, by themselves and alone, denote the locative case; while words like गौरी, formed in the way described already, give the sense of the locative, even alone, though they be placed anywhere in a sentence.,