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The melakha of Carrying is defined as moving an object from a private domain (reshut ha-yaĥid) to a public domain (reshut ha-rabim) or vice versa, or moving an object in a public domain more than four amot (six feet or a little less than two meters). What makes carrying unique is that an act that does not physically alter an object but merely changes its location in a significant way is still considered a melakha.
A public domain is defined as an area which belongs to the public and which anyone is entitled to use. Thus, a public domain represents the world, whose problems are largely due to division and dissension. Within a public domain there are different and competing interests at play, and therefore, moving items within it is an attempt to perfect or improve their position. This is forbidden. In contrast, a private domain is defined as a building or an area enclosed by walls and that belongs to one person or to partners. Thus, a private domain represents a perfected place. The enclosing walls give it a unity of purpose. All its rooms are considered to be in one place, within which items may be carried.
Most cities and towns in Israel have an eruv, which is a halakhic way to transform a public domain into a private domain, thus allowing people to carry items within the eruv. There are two components of an eruv. First, to define an area as a single private domain, it must be enclosed by a wall, a fence, or a tzurat ha-petaĥ (literally, the form of a doorway), meaning two posts with a string or wire running above them. Second, at least two meals-worth of food must be set aside on behalf of the community, generally by a rabbi who lives in the area. This connects all the residents together like one big family.
People who live in an area without an eruv, or are walking beyond the enclosed area, must make sure not to carry anything in their hands or pockets. This includes tissues, keys, and jewelry. It also includes carrying a baby or pushing one in a carriage. However, one may wear clothing, including shoes, hats, glasses, and a watch, as these are all considered secondary to the body. When it is absolutely necessary to carry identification or medicine, this may be done as long as the person makes a significant change in the way it is carried. For example, items may be placed under a shirt and held in place with a belt. Since carrying with a shinui is only rabbinically prohibited, one may be lenient when there is a very great need.
