I'm struggling to understand this also. Previous lessons seemed to indicate that if we wanted to day for example "good day" we would say היום הטוב... the ה needed to be prefixed to both words, otherwise it eould mean "a day is good". Now here, this seems to not be true anymore in this example, and I don't understand why.
I am not sure if you still need an answer to your question, but I figured I would answer since nobody else did. It goes like this:
first, the example you wrote: יום טוב - a good day היום הטוב - the good day
Then there are following examples: היום טוב - the day is good יום הוא טוב - a day is good
In this example: ספרים ארוכים - long books הספרים הארוכים - the long books
הספרים ארוכים - the books are long ספרים הם ארוכים - books are long
So, by putting or omitting ה the meaning of the sentence changes.
Not all books are long. Long books implies there are other types. Like black pepper, red hair, little girls. Now how you suggested, pepper is black (but there's white pepper, green pepper, etc), hair is red (not for most), girls are little. Only until they are big girls... so these books are long, (books can be long, but not all books are long... )
This feels somewhat clumsy, independent of which language is under consideration ...
- "sippoorrim arrookkim" ("long stories") - seems reasonable
- "sfarrim kvedim" ("heavy books") - likewise, fine.
But "long books" - trying to explain it away / show that it's perhaps not quite as clumsy a use of words as it appears to be - why do that?
Let's focus our efforts on constructing and learning sentences that are sensible on all levels ... or at least are unintentionally funny.