The fact is, the adjective is either adjective, adverb, or verb, according to occasion.

In the root form it also helps to make nouns; so that it is even more generally useful than as a journalistic epithet with us.

As a verb, it does duty as predicate and copula combined.

For such an unnecessary part of speech as a real copula does not exist in Japanese.

In spite of the shock to the prejudices of the old school of logicians, it must be confessed that the Tartars get on very well without any such couplings to their trains of thought.