office that they perform, are the _subject_ and the _predicate_. The
_subject_ is that about which something is asserted, and the _predicate_
is that which asserts something about the subject.

Some predicates may consist of a single word or word-group, able in itself
to complete a sentence: [The thrush _sings_. The thrush _has been
singing_]. Some require a following word or words: [William struck
_John_ (object complement, or object). Edward became _king_ (attribute
complement). The people made Edward _king_ (objective complement)].

The necessary parts of a sentence are: some name for the object of thought
(to which the general term _substantive_ may be given); some word or group
of words to make assertion concerning the substantive (general term,
_assertive_); and, in case of an incomplete assertive, one of the above
given completions of its meaning (object complement, attribute complement,
objective complement).

In addition to these necessary elements of the sentence, words or groups
of words may be added to make the meaning of any one of the elements more
exact. Such additions are known as _modifiers_. The word-groups which are
used as modifiers are the _phrase_ and the _clause_.

[The thrush, sings _in the pine woods_ (phrase). The wayfarer _who hears
the thrush_ is indeed fortunate (clause).]

Both the subject and the predicate may be unmodified:

[Bees buzz]; both may be modified: [The honey bees buzz in the clover];
one may be modified and the other unmodified: [Bees buzz in the clover].

The unmodified subject may be called the _simple subject_, or, merely, the
_subject_. If modified, it becomes the _complete subject_.

The assertive element, together with the attribute complement, if one is
present, may be called the _simple predicate_. If modified, it becomes the
_complete predicate_.

Some grammarians call the assertive element, alone, the _simple
predicate_; modified or completed, the _complete predicate_.

+16. Classification of Sentences as to Purpose.+--Sentences are classified
according to purpose into three classes: _declarative_, _interrogative_,
and _imperative_ sentences.

A _declarative_ sentence is one that makes a statement or declares
something: [Columbus crossed the Atlantic].

An _interrogative_ sentence is one that asks a question: [Who wrote
_Mother Goose_?].

An _imperative_ sentence is one that expresses a command or entreaty:
["Fling away ambition"].

Each kind of sen