ודבר דבר שלא יהא דבורך של שבת כדבורך של חול הילכך אסור לומר דבר פלוני אעשה למחר או סחורה פלונית אקנה למחר ואפי' בשיחת דברים בטלים אסור להרבות: הגה וב"א שסיפור שמועות ודברי חדושים הוא עונג להם מותר לספרם בשבת כמו בחול אבל מי שאינו מתענג אסור לאומרם כדי שיתענג בהם חבירו: (ת"ה סי' ס"א):

“Ve’daber davar” (teaches us) that one’s manner of speech on Shabbos must not be the same as one’s manner of speech on a weekday. Therefore, it is prohibited to say 'I will do such and such tomorrow' or 'I will purchase this and this merchandise tomorrow'. Even idle talk should be curbed. Rema: People who enjoy hearing stories or the latest news may speak these things on Shabbos but one who does not enjoy them may not speak them for the sake of giving pleasure to someone else.

It is prohibited to hire workers or to ask a Gentile to hire workers on Shabbos, even if the Jew only requires the work to be done after Shabbos. This is because everything that one is forbidden to do it is forbidden to tell a Gentile to do. It is also prohibited to ask a Gentile before Shabbos to do something on Shabbos. Nevertheless one is permitted to say to him after Shabbos “why did you not do so and so last Shabbos”, even though he will understand that one wishes he should do that particular Melacha next Shabbos.

It is prohibited to give money to a Gentile before Shabbos for him to make a purchase on Shabbos but one may say to him “purchase it for yourself and if necessary I will buy it from you after Shabbos.”

It is permitted to give money to a Gentile before Shabbos for him to make a purchase provided that one does not say to him “purchase it on Shabbos”. Rema: Likewise it is permitted to give him clothes to sell provided that one does not tell him to sell them on Shabbos. (Beis Yosef in the name of the Sma"g). One who hired a Gentile to transport merchandise and the Gentile arrived on Shabbos in order to take it from the Jew’s house, it is forbidden to allow him to take it and it is proper to punish the perpetrator. (Rabbeinu Yerucham).

One may instruct a Gentile to do an action that is not a Melacha but which is prohibited on account of a rabbinical prohibition, provided that it is needed in a case of minor illness, or it is greatly needed, or for the sake of a Mitzvah. For example, a Jew may instruct a Gentile to climb a tree to bring down a Shofar needed to blow for the sake of a Mitzvah, or to bring water through a yard that was not included in an Eiruv in order to wash someone suffering. There are those who prohibit it. Rema: Further in Siman 686 the Mechaber ruled that it is permitted, and see above in Siman 276 that there are those who permit it even for a Melacha de’Oraissa (work forbidden Biblically).

One may not calculate one’s expenses, even ones from the past. For example, to say I spent such and such an amount on something. However this is only when one must still pay the workers, but if one has already paid them it is permitted.

One may say to a friend that I am going to a certain town tomorrow, and one may also say come with me to a certain town tomorrow. It is permitted because it is possible to get there today by way of huts. The same applies to similar cases where there is a permissible manner to accomplish it today, one may instruct someone else to do it tomorrow provided that one does not mention his terms for hire. However, something that cannot be done today, even when it is only prohibited rabbincally, for example one has fruit that are muktze outside of the Techum, since it is not possible to bring them into the Techum it is prohibited to give instructions to bring them tomorrow. Likewise one may not position oneself at the end of the Techum in order to hurry and bring them after Shabbos. Rema: Likewise one may not say that one will do such and such tomorrow [Rosh, Perek HaShoel and see above at the beginning of the siman]. However, one may position himself at the end of the Techum in order to hurry and guard them because that could be done on Shabbos were they within the Techum. If one’s intention was only to guard them, then one may [position oneself at the end of the Techum] even [to] bring them.

One may say to a friend, look after my fruit that are within your Techum and I will look after your fruit that are within my Techum.

One who invited guests and prepared various dishes for them and one had written down the amount of guests and the amount of food he had prepared, it is prohibited to read the list on Shabbos, even if they are written high up on a wall, lest one reads documents i.e. bills and expenses. Rema: It is likewise prohibited to read them with one’s mind. (Rosh; R"an, Perek HaShoel; Tur) If however it is carved into the wall it is permitted, but reading from a tablet is prohibited even when carved into the tablet.

Regular documents such as bills and expenses and letters of greetings may not be read, and even to read them without expressing the words is prohibited.

One may read a letter that was sent to him if one does not know what it contains, one must not read the words aloud. If brought from outside the Techum it is correct not to handle it.

A wall or curtain with drawings of unusual animals or portrayals of people exhibiting a certain event, such as David and Goliath, and beneath it is a legend depicting it’s character, it is prohibited to read on Shabbos.

One may not read on Shabbos secular books of phrases and parables, books of passion such as Emanuel and war books. One may not read them during the week as well because it is a “sitting of scoffers” and because one is “removing Hashem from one’s mind”. Books of passion have an extra prohibition of arousing one’s evil inclination, and therefore the authors, the duplicators and of course the publishers cause the masses to sin. Rema: It is noteworthy that it is only prohibited to read secular writings and war books when they are written in foreign languages, but when written in Lashon Hakodesh it is permitted. That is what I see from Tosefos in Perek Kol Kisvei (Shabbos 116b), and people are accustomed to being lenient with this.

Anything other than Torah may not be learned on Shabbos and Yom Tov, and even books on humanities are prohibited; yet there are those that permit it. According to their opinion one may study the astrolabe on Shabbos (and also handle it, as written in Siman 308:50).