In the grammar textbook I've been reading, there is a class of partitive constructions called 'Partition in respect of quality' with an example as below:
a new kind of computer→ new kinds of computers
Why is it that the plural construction require both nouns to be in their plural forms while the singular one doesn't ? I find this intriguing because usually the count noun after of is in its plural form regardless of the partitive noun as in:
a kilo of apples
Interestingly enough, class seems to be a 'quality' partitive noun as well yet somehow a class of drug feels less appropriate than a class of drugs. I wondered if the former construction is actually acceptable and I'm just assuming things.
Edit: After looking up Webster's Dictionary of English Usage on page 576 (Webster's dictionary), it appears that there hasn't been a consensus regarding the structure of these constructions.
Please share your thoughts about this and if possible, about other similar but less common nouns in the screenshot below. (I took it from this website: Similar nouns)