24 Metarule: sixth case denotes substitution

We skip forward a few sutras to 1.1.49, which we have referred to previously as a metarule (see Post #3, January 2011):

1.1.49 şaşţhī sthāneyogā

The word division is as follows:

şaşţhī (1/1) sthāneyogā (1/1)

Thus both words are in first case (nominative), singular number. The first, şaşţhī, refers to terms in the sutras that are seen to be in the sixth case, which is the possessive or genitive: ‘of something’. The second word, sthāneyogā, tells us how to understand the possessive: i.e. as referring to ‘in place of’, rather than say ownership or proximity or part-whole relationship and so on. The vŗtti or paraphrase is rather involved, and only a sense of it can be got from the translation in Sharma or Vasu:

Iha śāstre (in this canon [the sutras]) yā şaşţhī (that in the sixth case) a-niyatayogā (? Not a fixed relationship) srūyate (? Which is heard), sā (that [sixth case])   sthāneyogā eva bhavati (is only the sthāneyogā), na anyayogā (not another relationship) sthāneyoganimittabhūte sati  sā pratipattavyā (?).

Formally,

"The force of the genitive case in a sutra is that of the phrase in the place of  when no special rules qualify the sense of the genitive“ (Vasu)

 “A genitive ending (which is not otherwise interpretable in its context) signifies the relation in place of” (Sharma).

The main point here is that the genitive case ending is interpreted in the sense of sthāneyogā, “in place of”  relationship. Thus, in the previous post, we discussed

ik 1/1 yaņah 1/1 (6/1?) samprasāraņam 1/1

where the second word is in the sixth case. So there it was interpreted as the sthāneyogā relation ‘in place of (y^aŅ, the semi-vowels)’, rather than, say, svaswāmi owner-owned  *‘of the y^aŅ’. Put together, it denotes ‘iK (short vowels) in the place of y^aŅ (the semi-vowels)’. The caveat is that the genitive or possessive (sixth) case should not be amenable to interpretation in a normal sense (i.e. other than this technical relation of sthāneyogā ‘in place of’) in the particular context.

Vasu (1891, p.36-37) seems to have somewhat more helpful explanations for this sutra. He suggests that the word  sthāna here has the sense of prasaŋga,  ‘occasion’, i.e. in the occasion of X, then Y, which then translates as ‘in place of’. In the sutra

2.4.52 Aster bhūh, the first word (removing sandhi), asteh,  is the possessive (sixth) case of asti; and the sense of the phrase would be, ‘in place of ast, (use) bhu’ as in forms such as bhavitā (future – will be), bhavitum (gerund – to be), bhavitavyam (passive participle – that has been).  

  

Vasu also unpacks the compound  sthāneyogā as a bahuvrīhi compound, where the first element sthāne is in seventh case (locative): that which has the relationship (yogā) denoted by sthāne (in the place).