Nouns are not just "persons, places, things/ideas". That's a poor definition. No kidding.
I peeked ahead and it seems the core is that it needs a shared semantic, morphological, and syntactic meaning (his words).
I think he's getting at they can be pluralized (yup). Only word class that can be pluralized. Count Nouns *vampire cackle*. But, not all nouns can be pluralized. Then he uses proper nouns to show that nouns can also be turned into possessives. But, again, not all nouns can become possessive ('happiness' for one). Non-Count Nouns *vampire cry*.
Conclusion - Only noun class words can be pluralized or turned possessive.
Verb time! Action words? Too vague. Verbs - they are the only words that can change form for tense.
Pronouns - Noun substitute? The corpulent elephant died. The corpulent it died? @_@ Nope. It died. It substitutes a noun phrase ("The corpulent elephant"), no matter the length of the noun phrase.
Conjunction (junction) - links words or phrases? @_@ Not exactly. It must link equal grammatical structure...and equal grammatical function. He gets a little intricate here in throwing out types of phrases. But the point is that the functions need to match.
End result - Procedures for testing types of words. Sounds good to me.
PS - Playing Touhou music in the background of any lecture makes it that much more awesome.