Is it Permitted to Mark a Page in a Book on Shabbat?

If a person is reading a book on Shabbat and wants to mark a page — for example, by lightly scratching the paper with a fingernail or folding the corner of the page, is this permitted?
 

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One of the prohibited labors on Shabbat is the act of writing. Anyone who writes even two letters on Shabbat is considered to have desecrated the day according to Torah law.

Making an Impression by Scratching Wood

In the Mishnah (Shabbat 103a), the Sages debate whether one who makes marks or scratches on wooden boards is liable for writing, or whether the Torah’s prohibition applies only to actual written letters.
According to Rabbi Yosei, even one who scratches a mark onto wood is liable because it constitutes a form of writing.

However, the Tur (Orach Chaim 340) rules not like Rabbi Yosei, and this is also the view of Rabbi Ovadiah of Bartenura, the Mishnah Berurah, and Maran in the Shulchan Aruch.

Nonetheless, the Sages prohibited this rabbinically — it is forbidden to make lasting marks or engravings on wood by scratching on Shabbat.

This leads to our question: If one lightly scratches paper with a fingernail to mark a place in a book, is that considered a form of writing or marking forbidden on Shabbat — or is it too temporary to count as a “real” mark?

Scratching Paper or Parchment on Shabbat

The Tur explicitly writes that it is permitted to make a small mark on paper or parchment with a fingernail on Shabbat. Maran the Shulchan Aruch (340:5) rules the same way.

Because such a mark is not permanent, as it fades over time, it is therefore not considered real “writing” or “engraving.” The rabbinic restriction only applies when the mark remains visible for a long time (like a deep scratch on wood), but a light scratch on paper fades quickly and is therefore allowed.

(However, it is forbidden to scratch or mark the skin on one’s body on Shabbat.)

The Difference Between Paper and Parchment

Some later authorities, including the Taz (Turei Zahav), argue that this leniency only applies to parchment, where the mark fades very quickly, but not to paper, where a scratch may last longer.

However, Maran’s wording in the Shulchan Aruch suggests that no such distinction was made. In his time, printed books on paper were already common, and yet he still permitted making light marks with a fingernail.

It is permitted on Shabbat to make a temporary mark on the edge of a page with a fingernail or to fold a page as a reminder, since such a mark does not last and is not considered “writing” according to Halacha.