Discuss parts of speech as Open and Closed Classes.

Open classes of words are the
classes that may continually be added to. For instance,
Verbs are an Open class of words because new verbs may be
created at any time and, in fact, are created all the time. "Texting" is a new verb
formed from the noun "text" as in the new compound noun "text message." Which points out
that Nouns are also an Open class of words. Other new nouns
or new meanings of old nouns are widget (1925-1930),
mouse (computer related useage), upquark, and
stranglet. Adjectives and
Adverbs are other Open classes of words as new adjectives
and adverbs can be and are created, though less readily than nouns and
verbs.

Closed classes of words
are those that do not change in terms of the collection of words therein.
Determiners are a Closed class of words: any,
some, a, each, etc. won't be added to.
Prepositions and Conjunctions
are the two other word classes that are Closed and that will not be added to. One
subgroup of words is also
Closed. The Pronoun subgroup of the
Noun class, which is Open, is another Closed class: we will not
have any new pronouns...unless discoveries of extraterrestial life forms demands
it.