GRAMMAR verb.

ROOT sentence.

PERSON :: first | second | third.
NUMBER :: singular | plural.

sentence: subject(PERSON, NUMBER), verb(PERSON,NUMBER).

subject(first, singular): "I".
subject(second, NUMBER): "you".
subject(third, singular): "he"; "she"; "it".
subject(first, plural): "we".
subject(third, plural): "they".

verb(first, singular): "walk".
verb(second, NUMBER): "walk".
verb(first, NUMBER): "walk", {NUMBER::plural}.
verb(third, NUMBER): "walk", {NUMBER::plural}.
verb(third, singular): "walks".
