1. There are roots and derivatives (deverbatives and denominatives) which form the thematic verb stems with -ie/-io, and the semithematics in -i. There can be an -a-, -e- or -e- preceding the suffix, sometimes as part of the Root or Derivative, sometimes as part of the suffix. We have then ie, -io, -aie, -aio, -eie, -eio, and even -aie, -aio; in these cases, the Root grade is usually Ø; as, bhudioti, he is waked up; but the full grade is also possible, as in spekio, look.
NOTE 1. The meanings in the opposition Basic Verb / Deverbatives, general in the Northern Dialects, are usually that of state or status; and also sometimes causatives and iteratives. There are also, as with those in consonant, examples of derivatives with -ie/-io without meaning, purely derivatives.
NOTE 2. The thematic inflection of these verbs is regular, and usually accompanied by the semithematic in the Northern Dialects, but not in the Southern ones, which do not normally combine them with -i, -e, or -a.
2. The thematic root verbs in -ie/-io are old, but have coexisted with the semithematics -ie/-io/-i/-i. These verbs are sometimes deverbatives (iteratives or causatives) or denominatives. The deverbative inflection could have -ie/-io, or -eie/eio, or the semithematic variant.
NOTE. The state or status value of these verbs is a feature of the Baltoslavic, mainly, with verbs in -e and -a, in which the inflection is sometimes combined with -ie/-io.
3. The stems in -u are rarely found in the Present, but are often found in the Imperfect and Perfect stems.
NOTE. The stems in -u have, thus, an opposed behaviour to that of the -i, which is usually found in Present and rarely in Imperfect and Perfect.
4. In Present stems, -u is found in roots or as a suffix, wether thematic or athematic (not semithematic), giving a stem that can also be the general stem of the verb: it is therefore a part of the root or a stable lengthening of it.
NOTE. Exceptions of this are gheu-/gho-, pleu-/plo-, etc.
5. Roots or stems with -e, with an athematic inflection and also mixed with -i. Sometimes the -e is part of the Root, sometimes it is a suffix added or substituting the -e of the Stem. They can be verbs without special meaning or verbs of state; as, albhe, be white, with stative value. There are also iterative-causatives; the denominatives are clearly derived from adjectives in -e/o.
NOTE. These are probably related with those in -i (i.e., in -eie/-eio, as in albheie, be white; moneio, remind, advise; seneio, be old ).
Athematic examples are lubhe, be dear, pleasing; rudhe, to blush, redden; gale, to call (not denominative). In some dialects they correspond to a thematic inflection in -eo.; as rudheo, to blush, redden (cel.) kapeo, have (ger., from kap, grasp).
6. Roots or stems with -a, athematic and mixed with -i. They are spread throughout the Verb system; as, bha (root), draw; duka, drag, draw; ghedisa, guess, etc. Also irregulars as lat. amo, possibly from -aio, but probably from -a without ending (like amas, amat,...).
About their Meaning, they are (specially in Latin) statives or duratives, and sometimes factitives opposed to statives in -e (clarare/clarere, albare/albere, nigrare/nigrere, liquare/liquere). But there are also many verbs without special value.
They form subjunctives, as well as preterites, and imperfectives. They are common Imperfects. To sum up, the tendency to make iteratives, statives and denominatives with -a is not so strong as with -e.
NOTE. There is, as with -e, a relation with -i, and there are also verbs in -aie/-aio.