Laws of the Three Weeks and Nine Days (4)
Learning Torah on Tisha B’av and for an Avel. In Tehillim, (19:9), Dovid HaMelech describes words of Torah as follows: "פקודי ה' ישרים משמחי לב" - the mitzvos of Hashem are just (see the Malbim’s explanation there) and give joy to the heart (of those who learn them). Therefore, the halacha states that an avel (mourner) during Shiva is not permitted to learn words of Torah (יו"ד שפ"ד). Similarly, on Tisha B’av, when all Jews mourn the destruction of the Bais Hamikdash, we are not permitted to learn Torah (או"ח תקנ"ד). This issur also applies to ladies who do not have the mitzvah of Talmud Torah. Even to think Torah concepts, which in many areas of halacha is not the same as actual learning (Birchas HaTorah, in front of ervah), is prohibited on Tisha B’av and for an avel because it too gladdens the heart (שם:ג). Children under the age of Bar Mitzvah should also not learn or be taught (שם:א).
Permitted Texts. There are certain texts relating to Tisha B’av and Aveilus which are permitted to be learned on this day of mourning. One may learn in a simple form without pilpul:
Megilas Eicha with all its Medrashim and commentators.
Kinnos said on Tisha B’av, laws of Tisha B’av, Aveilus, and Cheram (which is like Aveilus) in the Shulchan Aruch.
Parts of Tanach that talk about hardships: Iyov and Yirmiyahu (skipping posukim of comfort scattered throughout the sefer).
The entire third perek of Gemara Moed Katan; Gittin 55b-58a; Sanhedrin 96b-97a and 104b.
Works of Mussar according to many Poskim. The purpose of a fast day is self-improvement so this is desirable learning (תוס' חיים על חיי אדם קלה:ב, נחמת ישראל ל"ד).
Bitul Torah. There are numerous opinions about the issur of ביטול תורה on Tisha B’av. Shevat M’yehuda (יו"ד שפד:ד) and Kaf Hachayim (תקנד:י) hold that these are just permitted texts, but if one doesn’t learn them it isn’t ביטול תורה once Chazal prohibited regular learning. From the Chacham Tzvi (תשובה ק') it seems that since one has permitted texts, there is an obligation to study them and not to waste time.