Types of Speech on Shabbat

Our sages learn (Shabbat 113a) from the words (Yeshayahu 58:13) “Vedaber Davar” (lit. “and speaking words”) that one’s speech on Shabbat should not be the same as one’s speech on a weekday. Based on this, the Shulhan Aruch (O.H. 307:1) rules that one may not speak about doing something after Shabbat that is forbidden on Shabbat. For example, one may not say “tomorrow I will engage in such and such transaction or purchase” or the like. Furthermore, if there is another way to say something that does not include a forbidden act on Shabbat, one may say it. For example, since driving is not permitted on Shabbat, one may not say “tomorrow I will drive to such and such place” but one may say that one will simply go there or walk there, since those are permitted on Shabbat. 

The Mishna Berura (ibid:1) discusses whether one may speak about a forbidden labor which is for the purpose of a Mitzvah, such as saying that one will write a Sefer Torah after Shabbat. The Elya Rabba, Ma’amar Mordechai and the HIDA (Birke Yosef) write that there is room to permit speaking on Shabbat about an act which is for a Mitvzah. Some Sephardic Aharonim, such as the Ben Ish Hai (Parashat Vayishlah, 1) that one should be strict even regarding a Mitzvah, nevertheless, Rabbi OVadia Yosef (Hazon Ovadia, Shabbat, vol. V, pg. 57) writes that there is a Halachic basis to be lenient. 

The Rama (ibid.) adds that one who enjoys hearing stories or the latest news may engage in such speech on Shabbat. The Shelah Hakadosh (M.B. ibid ) explains that although it is permitted according to the letter of the law, it is not considered a pious act. The HIDA (Mahzik Beracha) concurs with the Shelah Hakadosh and adds that the Zohar (Beshalah) suggests that such speech is akin to desecrating Shabbat. It is written of the Arizal (Shaar Hakavanot ) that he only spoke Hebrew on Shabbat even if it was not related to Torah, but would only speak in foreign languages with others if such speech was related to Torah. 

Summary: On Shabbat, one may not talk about engaging in a forbidden Melacha after Shabbat, unless that Melacha is for the sake of a Mitzvah.