Some things in life change easily and often . They are fluid . They change and move as fluids do -- easily . When we are planning events or establishing rules and policies , sometimes it is good to keep things fluid or changeable . But some things are not easily moved or changed . They are fixed or inflexible . To describe these inflexible things , we can say they are set in stone . Things that are set in stone are very difficult or impossible to change . We can say that permanent rules , laws , and policies are set in stone . It often takes several difficult actions to change them . The dates of some events are also set in stone . For example , weddings take a lot of planning . Some people even start planning for their wedding a year or more ahead of time . You simply cannot tell friends and family that your wedding will happen sometime in June . You must find a space for the ceremony . You need to invite people and find out how many are coming . You need to decide on food , music , and flowers . And you must have money to pay workers to do different things . So , setting a wedding date in stone is the best way to make sure the wedding happens smoothly . Setting the date in stone means it cannot change . Or at least , changes would cause problems for people and possibly cost you a lot of money . We also use this expression with two other verbs : carve and write . So , you can say something is carved in stone or something is written in stone . The meaning stays the same . On the other hand , if a rule , date , or event could be changed easily , we can say it is penciled in . If you pencil something in , you are admitting that it is not set in stone . It may change and may be erased . When using this expression , however , you do not need to really use a pencil . For example , many workers were upset by some new office rules . So , the supervisor said , “If they don't work , we can always change them .” In other words , the rules are not carved in stone . It's good to have an editor with a sense of humor !