This is intended as a generic statement:
*A madrigal is popular.
This means that being popular is a requirement for being a madrigal.
...of course this conclusion is wrong, so I've marked the example with a star.
*A tiger is in danger of becoming extinct.
The tiger is in danger of becoming extinct.
Tigers are in danger of becoming extinct.
The Indefinite Generic a tiger is ungrammatical with the predicate become extinct, because that extinction can only happen to a species, and it means that every member is dead. In contrast, we we can use the Definite Generic because the predicate is characteristic of the species. We can also use a Plural Generic because we're speaking of tigers in aggregate.
I read those examples and explanations in a grammar book (or, more likely, online). Would anyone please explain those in a more simple way, so that I could get it? I cannot tell what the explanations mean very well.
Or could you possibly explain that with another example that is easier to understand?