May one open a book with letters or words written on the edges of the pages? (The words are seen when the book is closed).

In his respona the Rama addressed what seemed to be a common issue. It was customary to decorate a sefer with writing on the edges of the pages and hence the question was whether it is permitted to open such a book, thereby erasing letters, and shutting the book, thereby writing and reforming letters.

The Rama [1] and many others permitted this, saying that it is similar to the opening and the shutting of a door. Just as we do not say that opening or shutting a door is Boneh and Soter (construction and dismantling of the building) so too we do not say that one is writing or erasing when opening and shutting such a book because it is ‘created’ to do so.

On the other hand the Levush and the M”A held that one should not use such a book on Shabbos. [2]

The M”B states that the custom is in accordance with the Rama, but if possible to use another book without edge printing, one should use the alternative book. He concludes that one should definitely avoid printing such seforim in order to comply with all the poskim. [3]

Are there any cases where erasing will be beneficial and constructive and thus ossur mid’oraisso?

Besides the obvious case of erasing in order to be able to write in the place of the erroneous letters, there is another case. The P’ri Megadim writes [4] that erasing an IOU note that has been paid would be an issur d’oraisso, because it is beneficial. Usually erasing is destructive unless done with the intention of writing in its place, but in this case the erasure is beneficial on its own.

Is there an issur d’oraisso to write over existing letters?

The gemora says that it depends: writing with black ink over black ink is only an issur d’rabanan because one has not added anything; writing with black ink over red is an issur d’oraisso because of the added quality to the existing writing. [5] As it happens one is also violating an issur d’oraisso of erasing, by erasing the red ink beneath the black. It follows that if the original black ink has faded and one reinforces the writing one would be liable for violating an issur d’oraisso.

Why is it so important to know which writing is an issur d’oraisso and which d’rabanan, after all - all are prohibited?

There are a few answers to this question.

1) It is part of learning Torah. One’s Torah learning must be clear and precise.

2) One who violates an issur d’oraisso must bring a korban chatas. This carries implications nowadays even though there is no Beis Hamikdash with respect to giving tzedaka (charity) the equivalent of a korban. Also, we find in the gemora that one of the Tana’im violated an issur d’oraisso unintentionally and said that he must write in his notebook that when the Beis Hamikdash will be rebuilt he will bring a korban chatas.

3) It is sometimes necessary when dealing with pikuach nefesh (life saving) to write down crucial details. In an emergency situation of dire proportions one would write in the normal fashion -  that is a with a normal writing implement on paper etc., but when the situation is not critical, even though writing is imperative, one should try and find other methods of writing which will not involve the violation of an issur d’oraisso.

Name a practical example of writing that is not a d’oraisso.

A right-handed person writing with his left had is only violating an issur d’rabanan. [6] Therefore, if time permits, one should write with one’s left hand.

Writing with self-erasing ink, according to some poskim [7] is only an issur d’rabanan. This is because we learnt in the last shiur that one of the criteria for writing to be an issur d’oraisso is for the writing to be long lasting. One would therefore write on Shabbos with self erasing ink and copy it down after Shabbos.

Although writing a single letter is an issur d’oraisso [8] nevertheless one is only liable to bring a korban for writing two letters. Therefore, when possible (and extremely necessary) one would write a letter with an apostrophe, such as î', which is not considered as writing a word (or even two letters) even though it is understood what is meant.