Do you mean different from each other? Fundamentally it's a matter of
phonetics: certain weak consonants were lost between vowels after which the
vowels contracted to form a spurious diphthong or a long vowel. It's a
matter of what elements are contracting. One may say generally that O
vowels prevail over both A and E vowels, and A vowels prevail over E vowels
(but when we have A + E, the result is long A, which changed way back when
into H). One of the trickier things is the fact that O + E, E + O, and O +
O all yield the spurious diphthong OU; what happened is that the result of
each of these combinations after contracting was a long closed O which was
spelled OU (but probably originally pronounced more like the OW in "blow").
But this is why OW verbs and EW verbs have common forms in those endings
consisting of a stem ending in E or O + thematic vowel (O/E): all these
contractions of EO, OE, OO will yield OU; on the other hand EE will yield a
spurious diphthong spelled EI, a long closed E (but probably originally
pronounced like EY in "they").
As far as uncontracted verb forms are concerned, you're most likely to see
an uncontracted 1st sg of a contract verb most frequently in a lexicon and
you're not likely to see it anywhere else. It's spelled in an uncontracted
form there simply in order to let the user see what the stem vowel is so as
to know what contractions to expect in the rest of the morphology. One sees
uncontracted forms in Ionic dialect, e.g. in Herodotus or in the fragments
of Heraclitus or in some of the early Ionian lyric and elegiac poets; in
Homer one sees "resolved" contractions such as hOROWSI(N) for
hORWSI(N)--the original form before contraction would have been hORAOUSI
(or to be more precise hORAONTI), but when Homer wants two syllables he
stretches out the O-sound just as we do in singing a vowel that has to
stretch over two or more beats--this is the impact of the meter on
pronunciation.
I'm not sure whether this answer fits your particular question, but if it
doesn't, you can try again.
Carl W. Conrad
Department of Classics/Washington University
One Brookings Drive/St. Louis, MO, USA 63130/(314) 935-4018
Home: 7222 Colgate Ave./St. Louis, MO 63130/(314) 726-5649
cwconrad@artsci.wustl.edu OR cconrad@yancey.main.nc.us
WWW: http://www.artsci.wustl.edu/~cwconrad/