421. The stem has a triple form

The stem has a triple form. In the strong cases of the masculine, the vowel of the ending is prolonged to आ ā; in the weakest cases it is in general struck out altogether; in the middle cases, or before a case-ending beginning with a consonant, the final न् n is dropped. The न् n is also lost in the nom. sing. of both genders (leaving आ ā as final in the masculine, अ a in the neuter).

a. The peculiar cases of the neuter follow the usual analogy (311 b): the nom.-acc.-voc. pl. have the lengthening to आ ā, as strong cases; the nom.-acc.-voc. du., as weakest cases, have the loss of अ a — but this only optionally, not necessarily.

b. In the loc. sing., also, the a may be either rejected or retained (compare the corresponding usage with -stems: 373). And after the m or v of man or van, when these are preceded by another consonant, the a is always retained, to avoid a too great accumulation of consonants.