It is a mitzva to honor Shabbat in the way one speaks, as it is written: “and if you honor it, and not go in your own way, nor look to your affairs, nor speak of them” (Yeshayahu 58:13). The Sages elaborate: “‘Nor speak of them’ – your speech on Shabbat should not be like your speech on weekdays” (Shabbat 113a). This means that one should not speak on Shabbat about things that one may not do on Shabbat. Therefore, one should not say, “Tomorrow I will travel by car,” “I will write a letter,” or “I will buy an item.” Clearly, then, it is also prohibited for one to ask someone else to travel the next day on his behalf, write a letter for him, or buy something for him (SA 307:1). This prohibition applies to things that one intends to do in the future. However, one may speak about what he has already done, as long as he does not intend to provide useful information to the listener on how best to perform the melakha.
The prohibition applies to talking about actions prohibited on Shabbat. In contrast, one may think about them. Thus the Sages expound: “Speaking [about mundane matters] is forbidden, but thinking about them is permitted” (Shabbat 113a). Speech that merely alludes to a melakha is considered “thinking” and is thus permitted. For example, while one may not say, “Tomorrow I will phone so-and-so,” one may say, “Tomorrow I will speak with so-and-so,” even though it is clear that he will do so by phone. Similarly, one may not say, “Tomorrow I will drive to Jerusalem,” since traveling by motor vehicle is prohibited on Shabbat, but one may say, “Tomorrow I will go to Jerusalem,” since one can “go” by walking, and even though Jerusalem is outside the teĥum, theoretically one could build an eruv to Jerusalem and it would be permitted to walk there on Shabbat. Since walking to Jerusalem is not fundamentally prohibited, one may talk about “going” there. Even if the listener realizes that the speaker means that he is planning to travel by car or bus and that the listener may join him if he wishes, the statement is still considered only a hint and is permitted.
Similarly, if one plans to travel by cab after Shabbat, on Shabbat he may ask his friend who is a cabdriver, “Do you think you will be able to come over after Shabbat?” Since he has not asked his friend to come with his cab in order to drive him, then even though his friend understands that this is what is meant, it is not prohibited. However, he may not say to his cabdriver friend, “Come over after Shabbat, please,” because an allusion in the imperative form is prohibited. Following the same principle, one who wishes to hire a worker on Sunday may say to him on Shabbat, “I hope to see you on Sunday,” but he may not say, “Please come on Sunday” (Shabbat 150a; SA 307:7).
One may not speak about monetary transactions that have business implications, while one may talk about them if they have no practical import. Therefore, one may not speak about wages owed to workers, but one may speak about wages already paid. Similarly, one may not tell another how much a house sold for if the listener is interested in buying a similar house, while one may pass on this information to someone who is not interested in buying a home. Likewise, one may report on how much yield a field produced the previous year, what the government’s budget is, and the like. This is because the people involved in these conversations have no plans to act on these discussions during the week (SA 307:6).
It is preferable to minimize trivial conversations on Shabbat. One who enjoys such conversations may engage in them a bit more than usual, as they are part of his physical enjoyment of Shabbat. However, he should not indulge himself excessively, just as he should not eat or sleep excessively, as these indulgences will take away from the time he needs to set aside for Torah study on Shabbat. We have already seen that a minimum of six hours must be dedicated to Torah study on Shabbat (SA and Rema 307:1; MB ad loc. 4; see above 5:1).