I have been wondering why "Books I read yesterday were interesting" sounds odd to native speakers of English. So have my friends.
Let me confirm if the following understanding is correct:
1. A book (that) I read yesterday was interesting.
This sentence structure is possible. The sentence means: A book (One book) was interesting. I read it yesterday.
Similarly, the sentence "Some books (that) I read yesterday were interesting," is possible and it means: Some books were interesting. I read them yesterday.
2. The book (that) I read yesterday was interesting.
People don't start a conversation by saying, "The book was interesting," unless there is an appropriate context because the listeners don't know what "the book" refers to.
The relative clause in the above sentence explains what "the book" refers to. The sentence means: I read a book yesterday. The book was interesting.
Similarly, the sentence "The books (that) I read yesterday were interesting," is possible and it means: I read some books yesterday. The books were interesting.
3. Books (that) I read yesterday were interesting.
This sentence structure is impossible. People don't start a conversation by saying, "Books were interesting," or otherwise it sounds as if books in general were interesting.
4. I read a book/some books (that) he gave me.
This sentence structure is possible and it means: I read a book/some books. He gave it/them to me.
5. I read the book/books (that) he gave me.
Again, people don't start a conversation by saying, "I read the book/books," unless there is an appropriate context.
The relative clause explains what "the book/books" refers to. The sentence means: He gave me a book/some books. I read the book/books.
6. This is the book (that) you lost last week.
People don't start a conversation by saying, "This is the book," unless there is an appropriate context because the listeners don't know what "the book" refers to.
The relative clause in the above sentence explains what "the book" refers to. The sentence means: You lost a book last week. This is the book.
7. This is the book (that) I bought yesterday.
This sentence structure is possible and it means: I bought a book yesterday. This is the book.
8. This is a book (that) I bought yesterday.
This sentence structure is possible but it occurs less frequently than sentence structure 7, because people don't start a conversation by saying, "This is a book," because the listeners will know it is a book when they see it.
However, "This is a box of candy (that) I bought yesterday," may occur more frequently because the listeners may not know what is in the box. This sentence means: This is a box of candy. I bought it yesterday.