We have found that with the incomplete verbs of state or condition, or
copulative verbs, the predicate complement may be either a noun, as,
_The man is a hero_; or an adjective, as, _The man is class-conscious_;
or a phrase, as, _The man is in earnest_.
The predicate complement may also be:
+431.+ +A pronoun+; as,
Who is she?
That was he.
This is I.
In these sentences the subjects of the verbs are _she_, _that_ and
_this_, and the pronouns _who_, _he_ and _I_ are used as predicate
complements.
+432.+ +Infinitives may also be used as the predicate complement+, thus:
To remain ignorant is _to remain_ a slave.
_To remain ignorant_, is the subject of the copulative verb _is_, and
the infinitive, _to remain_, with its complement, _a slave_, is the
predicate complement.
+433.+ +A participle used as a noun may also be used as the predicate
complement+, thus:
Society is the mingling of many elements.
_Mingling_, in this sentence is a participle of the verb _mingle_, but
is used as a noun, the predicate complement of the verb _is_. _Society_
is the subject of the verb.
Where the present participle is used to form a verb phrase, the
participle is part of the verb phrase, thus:
We are mingling in society.
Here, _are mingling_, is the present progressive verb phrase, and the
participle _mingling_ is not used as a noun or adjective, but is part of
the verb phrase _are mingling_.
If you will observe the different parts of speech carefully, you will
not be easily confused as to whether the participle is a noun or a part
of the verb phrase.