The Cambridge Introduction to Sanskrit

Below are the paradigms of four nouns that employ regular consonant-stem endings (and in a few cases vowel-stem alternatives). They all have stem gradation, and the cases one would expect to be strong are so (NOMVOCACC SG and DU, NOMVOC PL) and the rest weak; yet they alternate either between vṛddhi and guṇa (1, 2) or vṛddhi and zero grade (3, and in a sense 4).

गो- ‘BULL’; ‘COW’

गो- may be masculine (and thus have masculine adjectives or pronouns referring to it) and mean ‘bull’; or it may be feminine and mean ‘cow’. Its strong stem stands in vṛddhi (gau- = gāv- before vowels), its weak stem in guṇa (go- = gav- before vowels). Yet note two unexpected forms: in the ACC SG, the -u- is dropped, resulting in गाम्; and its ACC PL is गाः.

द्यो- ‘SKY’

This noun shows the same stem variation as गो- – vṛddhi in the strong cases (-au- before consonants, -āv- before vowels), guṇa in the weak cases (-o- before consonants, -av- before vowels), and a dropped -u- in the ACC SG द्याम्. Finally, note the ACC PL There is also a parallel paradigm that simply has zero-grade in all forms except for the NOMVOC SG (these appear as div- before vowels and dyu- before consonants). This second, more regular paradigm is actually more frequent in Classical Sanskrit.

पथ्- ‘PATH

The strong forms of this noun are doubly marked. Not only do we find the guṇa of the stem (panth-, as opposed to zero-grade path- in the weak forms), but we also find a suffix (-ān-) that is absent in the weak cases. Hence, the ACC SG is panth-ān-am, while the ACC PL is path-o-aḥ. The NOM SG does not have the 2nd nasal, and its ending appears just as -āḥ. In weak cases whose ending begins with a consonant, an -i- appears between the weak stem and the ending, giving us path-i-bhiḥ etc.