824. The final vowel of a tense stem is said to be _variable_ when it is
#-o-# in some of the forms, and #-u-#, #-e-#, or #-i-# in others.
825. The sign for the variable vowel is #{-o|e-}#: thus, #reg{o|e-}#,
which may be read ‘#rego-# or #rege-#,’ represents #rego-# or #regu-#,
#rege-# or #regi-#, as seen in #rego-r# or #regu-nt#, #rege-re# or
#regi-t#.
826. The variable vowel occurs in the present of verbs in #-ere#, except
in the subjunctive, in the future in #-bō# or #-bor#, and in the future
perfect, as may be seen in the paradigms. It is usually short; but in
the active, #o# is long: as, #regō#, #laudābō#, #laudāverō#; and poets
rarely lengthen #i# in the second and third person singular of the
present. For the future perfect, see 882.
827. In old Latin, the stem vowel of the third person plural of the
present was #o#: as, COSENTIONT; #o# was long retained after #v#, #u#,
or #qu# (107, _c_): as, #vīvont#, #ruont#, #sequontur#; or, if #o# was
not retained, #qu# became #c#: as, #secuntur#.