ダンスの先生なんだから、上手なはずですよ


ダンスの先生なんだから、上手なはずですよ。 is はずです is work as a noun here ?? as its attached after
na adjective




Yes, grammatically speaking, this はず is working as a noun, and dictionaries
indeed categorize it as a noun. This noun on its own means something like
"natural consequence/estimation":

  * 上手な: good (at dancing)
  * はず: natural estimation

Of course "goodness's natural estimation" makes no sense in English, and the
sentence is normally translated like "he/she must/should be good at dancing".

  * [Maggie Sensei: How to use はず ( = hazu)](http://maggiesensei.com/2012/11/14/request-lesson-how-and-when-to-use-%E3%81%AF%E3%81%9Ahazu/)
  * [Tae Kim's Guide to Learning Japanese: Things that should be a certain way](http://www.guidetojapanese.org/learn/grammar/should)

A noun like this is called a 形式名詞 ("formal noun"). Instead of working as an
ordinary noun, they play some grammatical role, and it's often hard to
translate them using English nouns. Other 形式名詞 include とき ("when"), こと
(nominalizer), うち ("during"), とおり ("as/like") and の (explanatory-no).
Practically speaking, English speakers may want to just memorize the patterns,
rather than worrying too much about their meanings as nouns.

