Example 1:
Three gangsters, whose names are unknown, robbed a bank.
We talk about three gangsters and we use plural form. Everything is clear here.
Example 2:
Consider the following passage from a hypothetical grammar book, or maybe corporate style guide for in-house writers.
- With simple sentences - use a comma.
- With complex sentences and in cases when the type of sentence is unknown - use semicolon.
Here, only the second part is the subject of my interest:
- With complex sentences and in cases when the type of sentence is unknown - use semicolon.
We say "in cases" (plural) because it's not one, single case. There could be different cases. So we use plural form. Okay.
But then, we say "type of sentence" (singular). Why? Isn't it very illogical? Why we use singular form after plural?