19. When the adjective is a part of that which is told or predicated of
the subject of the verb, as when used with the verbs "to be," "to seem,"
etc., it is called a "predicate adjective":
La birdo estas bela, the bird is beautiful.
La knabo sxajnas bona, the boy seems good.
La viroj estas fortaj, the men are strong.
20. A noun may also be used as part of the predicate, and is then called
a "predicate noun":
Violoj estas floroj, violets are flowers.
La kolombo estas birdo, the dove is a bird.
21. Predicate nouns and adjectives agree in number with the word
or words with which they are in predicate relation:
Rozoj estas belaj, roses are beautiful.
La knabo kaj la viro sxajnas fortaj, the boy and the man seem strong.