1740. Subordinate subjunctive sentences were originally independent
coordinate sentences, in the tense required to express the thought. By
degrees the subordinate sentence blended closely with the main sentence,
and the combination of the two was regarded as one whole.
1741. I. The time of the subordinate subjunctive is usually _Relative_,
that is either contemporaneous, antecedent, or subsequent, in relation
to that of the main action.
1742. Action contemporaneous with the main action is expressed by a
present or imperfect subjunctive. Action antecedent is expressed by a
perfect or a pluperfect subjunctive. Action subsequent is expressed by
the future participle with a form of #sim# or of #essem#.
1743. Subordinate sentences with verbs of will or aim, with verbs of
fear, also final sentences and many consecutive sentences are expressed
in Latin as contemporaneous with the main action, not as subsequent to
it.
1744. II. The main and subordinate sentences may express wholly
different spheres of time by tenses not commonly used together, when the
thought requires it. In such cases the tense of the subordinate member
is called _Independent_, like the analogous tenses of the indicative
(1738).
1745. The use of subordinate subjunctive tenses relatively to the main
tense, or what is commonly called the _Sequence of Tenses_, is as
follows: