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.