877. We have, then, the following classification for the varieties of sibilant-aorist:
A. With endings added directly to the sibilant:
4. with स् s simply after the root: s-aorist;
5. with इ i before the स् s: iṣ-aorist;
6. the same, with स् s at end of root: siṣ-aorist.
B. With अ a added to the sibilant before the endings:
7. with sibilant and अ a: sa-aorist.
a. As regards the distinction between the fourth and fifth forms, it may be said in a general way that those roots incline to take the auxiliary i in the aorist which take it also in other formations; but it is impossible to lay down any strict rules as to this accordance. Compare 903.
4. The s-aorist.
878. The tense-stem of this aorist is made by adding स् s to the augmented root, of which also the vowel is usually strengthened.
879. The general rules as to the strengthening of the root-vowel are these:
a. A final vowel (including ऋ ṛ) has the vṛddhi-change in the active, and (excepting ऋ ṛ) guṇa in the middle: thus, from √नी lead, active stem अनैष् anāiṣ, middle stem अनेष् aneṣ; from √श्रु çru hear, अश्रौष् açrāuṣ and अश्रोष् açroṣ; from √कृ kṛ make, अकार्ष् akārṣ and अकृष् akṛṣ.
b. A medial vowel has the vṛddhi-change in the active, and remains unaltered in the middle: thus, from √छन्द् chand seem, active stem अच्छान्त्स् acchānts, middle stem अच्छन्त्स् acchants; from √रिच् ric leave, अरैक्ष् arāikṣ and अरिक्ष् arikṣ; from √रुध् rudh obstruct, अरौत्स् arāuts and अरुत्स् aruts; from √सृज् sṛj pour out, अस्राक्ष् asrākṣ and असृक्ष् asṛkṣ.
880. a. The endings are the usual secondary ones, with उस् us (not अन् an) in 3d pl. act., and अत ata (not अन्त anta) in 3d pl. mid.
