inted_ it yesterday,"
not "I _have printed_ it yesterday;" "I _have not_ yet _printed_ it,"
not "I _did_ not _print_ it yet;" "I _have printed_ it already," not "I
_printed_ it already."

Trouble is sometimes found in choosing the right forms of the verb to be
used in subordinate clauses. The rule is:

Verbs in subordinate sentences and clauses must be governed by the tense
of the principal verb.

This rule rests on the exact meaning of the forms and words used and its
application can be checked by careful examination of these meanings. "He
_said_ he _did_ it." "He _said_ he _would do_ it." "He _says_ he _will_
do it."

Note that when the statement in the subordinate clause is of universal
application the present tense is always used whatever the tense of the
principal verb. "The lecturer said that warm weather always softens
rollers."

Those forms of the verb which tell whether the action is an actual fact,
a possibility, a condition, or a command are called moods.

There are three moods, the indicative, subjunctive, and imperative.

The indicative mood indicates that the action is a fact. It is also used
in asking questions.

The subjunctive mood is less used in modern than in old English. It is
most commonly found in clauses beginning with _if_, though _if_ is not
to be regarded as the sign of the subjunctive in any such sense as _to_
is the sign of the infinitive.

The subjunctive _were_ should be used in purely hypothetical clauses
such as "If I were in your place."

The subjunctive _be_ should be used in the hypothesis or supposition of
a scientific demonstration,

If the triangle A be placed on the triangle B.

The subjunctive without _if_ is often used in wishes or prayers,

God forgive him.

O, that my brother were here.

The subjunctive is sometimes used to express condition,

Had you not been a coward, you would not have run away.

The imperative mood indicates a command,

Put that on the press.

The subject of the imperative mood is only expressed when it is
emphatic,

Go thou and do likewise.

Older grammarians speak of a fourth mood called potential. The present
tendency among grammarians is to treat these forms separately. They are
verb phrases which express ability, possibility, obligation, or
necessity. They are formed by the use of the auxiliary verbs _may_,
_can_, _must_, _might_, _could_, _would_, and _should_, with the
infinitive without _to