- Some people think that the rich don't pay enough tax.
- Some people think that the rich people don't pay enough tax.
In sentence (1) we have a determiner plus adjective combination, where the is the determiner and rich is the adjective. According to writers like Huddleston & Pullum et al (The Cambridge Grammar of the English Language 2002) this is a type of Noun Phrase - even though, as they say, it has no nouns in it!
We can clearly show that rich is an adjective here, not a noun. Most importantly, we cannot use adverbs to pre-modify nouns, but we can use them with adjectives:
- a very big lion
- the very rich
- *a very banana (ungrammatical)
There does not seem to be any limit to the type of adverbs we can use to modify rich in this way:
- The unexpectedly rich
- The quietly rich
- The extremely rich
- The brazenly rich
All of the above can function as the subjects or objects of sentences and are perfectly grammatical.
This type of construction must have the determiner the. If it does not, the sentence will be ungrammatical:
- *Rich don't pay enough tax. (ungrammatical)
- *Some rich don't pay enough tax. (ungrammatical)
In sentence (2) rich is an adjective modifying the noun people. This sentence is grammatical. However, at the moment it does not mean exactly the same as sentence (1). The reason is that, when we want to talk about things in general, we do not use the definite article with normal Noun Phrases. We use no article at all:
- Love is the most important thing in life.
- *The love is the most important thing in the life. (ungrammatical or a very strange meaning)
At the moment sentence (2) doesn't refer to rich people in general. It refers to a specific group of rich people. We know this because it uses the definite article the. Maybe it is referring to the rich people in a particular town, or the rich people in the entertainment industry. It isn't talking about people in general though. If we want to make the sentence have a similar meaning to sentence (1) we need to remove the article:
- Some people think that rich people don't pay enough tax.
Notice that the grammar for this sentence is different from sentence (1). We can use constructions like the rich or the lucky to refer to rich people in general or lucky people in general.
Hope this is helpful!