1. The athematic Imperfect Root stems, opposed to athematic Reduplicated Presents, are not the only possible athematic roots. There is no root ending in consonant, though.
2. In monosyllabic Roots we have an opposition of:
a. A Present in -neu; as, klneu / kleu, to hear; qrneu / qer, to make, do; etc.
b. A Reduplicated Present or with -ske/-sko or -io: caske / ca, go; bhesko / bhes, breathe; etc.
c. A Thematic Present: ghewo / ghew, pour; bhawa / bhut, proclaim, ban.
3. Disyllabic roots present similar behaviours: gignosko / gno , bhalio / bhle , etc.
The theme vowel system is the usual: Present Singular Active with full vowel, and Ø in the rest.
NOTE. Disyllabic Roots tended to generalize a unique form (as gno-, bhle-, etc).
4. The Thematic Imperfect Roots are also those of the Present, bhere/o and bhre/o, opposed to any Present.
a. It is the bhre/o form that which is found mostly in the Imperfect;
b. The bhere/o form is rarely found, but when it is found the Present has to be logically different.