714. The stem contains the meaning of the verb, and also denotes the
mode (mood) and the time (tense) of the action as viewed by the speaker.
715. There are three MOODS, _Indicative_, _Subjunctive_, and
_Imperative_.
716. There are six TENSES in the indicative, three of the present
system, _Present_, _Imperfect_, and _Future_; and three of the perfect
system, _Perfect_, _Pluperfect_, and _Future Perfect_. The subjunctive
lacks the futures; the imperative has only the present.
717. The meanings of the moods and tenses are best learnt from reading.
No satisfactory translation can be given in the paradigms, especially of
the subjunctive, which requires a variety of translations for its
various uses.
718. The verb has two principal stems: I. The Present stem, which is the
base of the present system; II. The Perfect stem, which is the base of
the perfect active system.
719. The perfect system has no passive; its place is supplied by the
perfect participle with a form of #sum#, _am_, or less frequently of
#fuī#, _am become_.
720. Many verbs have only the present system: as, #maereō#, _mourn_;
some have only the perfect system: as, #meminī#, _remember_. Some verbs
have a present and perfect system made up of two separate roots or
stems: as, present indicative #ferō#, _carry_, perfect indicative
#tulī#, and perfect participle #lātus#; present #possum#, _can_, perfect
#potuī#.