Why is there an entire Death Note if only one page is enough?

Question

After discussing the matter of whether the Death Note will ever run out of pages, it appears to me that there is another unclear matter, which is whether the page itself can ever run out?

You can easily take a page, use an erasable pen and write carefully, then when filled, erase the entire writing without damaging the page. You will always be able to kill other people using that same page. I have the following sub-questions:

1. Is this even possible, that is, can you kill people after writing on an erased page?
2. When do we say that the Death Note has run out? See the picture below¹, which says that when you run out of room to write, you can ask your Shinigami to bring you another Death Note.
3. If I fill my note, ask the Shinigami for another one, then erase what was written on my first note, will I have made two Death Notes for myself?
4. If the above is true, and since the rules imply that no more than six Death Notes can be brought to the human world, why didn't Yagami Light do that to get six Death Notes, ensuring that no one else gets a Death Note?
5. How does the Shinigami tell that the Note is filled or not? Does he just look at the pages and see whether they are written or not?

---

¹ Death Note Manga Pilot, Chapter 0, page 26.

Answer 1

It says that when you run out of room to write you can ask your Shinigami to bring you another Death Note.

The manga pilot is non-canon. However, nothing is explicitly stated about it in the main series, so this rule may or may not be valid for the main series.

• Rule is not valid in the main series.

  In this case, the Death Note somehow "grows" more pages once you use up all the pages, as described in this answer.

  • How does the Shinigami tell that the Note is filled or not?
  • When do we say that the Death Note had run out?
  • What if I fill my Note, ask the Shinigami for another one, then erase what was on my first Note again, will I have made two Death Notes for my self?
  • Why didn't Yagami Light do that to get six Death Notes?

  Under this assumption, these questions are not applicable.

• Rule is valid in the main series.

  • How does the Shinigami tell that the Note is filled or not?
  • When do we say that the Death Note had run out?

  Just like how we, in real life, tell if a notebook is filled or not! If the owner tells the Shinigami that the notebook is filled, they would probably glance over the pages to see if all pages appear to be filled up, or maybe, they won't even bother doing that, and just hand over a new notebook.

  It has been explicitly stated and seen that the Shinigami are generally lazy and not very smart. I cannot picture them telling the owner, "Hey look, there's a little space here in the corner, why don't you write there for now?"

  • What if I fill my Note, ask the Shinigami for another one, then erase what was on my first Note again, will I have made two Death Notes for my self?
  • Why didn't Yagami Light do that to get six Death Notes?

  The assumption here is that either the owner hands over their used notebook and then gets a new one, or the used notebook becomes ineffective and is excluded from the count. This is a reasonable assumption because otherwise there would be a contradiction when Light asks Ryuk for a 7th notebook.

Can you kill people after writing on an erased page?

There's a Death Note rule regarding erasing names:

How to Use: XLII

1. It is useless trying to erase names written in the Death Note with erasers or white-out.

The word useless in the above rule could be interpreted to mean either of two things:

1. Don't bother trying to erase a name in the hope of saving the person whose name you just wrote because that isn't going to work.
2. Erasing itself isn't going to work. Anything written in the Death Note cannot be physically erased.

If the interpretation 2 is correct, end of discussion, obviously. If interpretation 1 is correct, you could theoretically keep reusing the pages by writing with pencil and erasing with an eraser, or writing with ink and washing it with water, etc. However, it is probably not worth the trouble because you have endless pages anyway.

Lastly, to answer the title question:

Why there is an entire Death Note while only one page is enough?

For convenience, that is all. With more pages, you can avoid the hassles of having to erase every few days, erasing with care to prevent damage to the page, etc. Moreover, the Death Note was not "designed for humans", it was "designed for Shinigami". The product design generally caters to the preferences of its primary customer base. :-)