Can "rich" and "poor" be used as nouns?
He was adored by rich and poor alike.
This sentence is from my textbook. I'm thinking why not "the rich and poor alike"? (the + adj.) Also, if "rich" and "poor" are nouns here, why not "riches" and "poors"?

Thank you!

Question

Can "rich" and "poor" be used as nouns?
He was adored by rich and poor alike. 
This sentence is from my textbook. I'm thinking why not "the rich and poor alike"? (the + adj.) Also, if "rich" and "poor" are nouns here, why not "riches" and "poors"?

Thank you!

Answer

Poor
exists as a collective noun and has to be preceded by 'the'.
The poor
It doesn't have a plural 'poors'.

Rich
The same goes for 'rich'
The rich
'Riches' exist as a plural noun and means wealth, an abundance of money or property.

Answer

I would have to agree with you on the "the rich and poor alike" part.
In this context, the rich (and the poor) refer to a group of people so you don't need to add the "es" or "s".
I believe there's no such word as poors.

Answer

You can use "the rich'' and "the poor" to refer to people who are rich or poor. The nouns for "rich" and "poor" are "richness" and "poverty".