For example, the property law of socialist countries is based on the idea that the property should be held for the benefit of all citizens rather than for the benefit of particular individuals. In these countries, only the government can own the “means of pro-ductionw. In capitalist societies, on the other hand，the means of production are owned by individuals. Capitalists generally believe that the common good is advanced when individual self-interest is channeled toward the common good, perhaps indirectly1. The law of the United States recognizes private ownership of property.

Several classes of property are recognized by the property law. These classes generally determine which particular body of law will govern the ownership，transfer of ownership» taxation and financing of the property2. The major categories of property are real property, personal property, and intellectual property.

Real property (or realty) is land and things immovably attached to the land. The basic test for identifying real property is whether a tangible thing is movable in a practical sense. A house can be moved，but because it requires a great effort to do so, the law views it as immobile. Similarly, something permanently attached to a house, such as an under-the-counter dishwasher, is viewed as immobile9 and is therefore real property.

Personal property, or personalty, is something that is both tangible and mobile. Cars, ships, shoes，suits, and watches are tangible and mobile. Thus they are personal property. Many items change legal status with differing uses. For example, wood is realty while still part of a tree in the ground, personalty when cut into studs, and realty when nailed into the fence of a house under construction. Since tangible property can change status ,the law has evolved other tests besides mobility to distinguish real and personal property in close cases. They are tests of annexation，adaptation and intention.

The annexation test is a refinement of the basic test of mobility. If something tangible is permanently attached to realty，it is considered a part of the realty. If it is not permanently attached to the realty, then it is mobile and usually considered personalty. Structures or buildings are part of the real property only if they are permanently attached to the land. Thus, a house trailer sitting on its wheels is usually considered personal property. If the removal of a thing from a structure damages the structure, the thing is probably realty. A freestanding store is personalty, but a built-in store is realty under the test of annexation.

The importance of a thing to the functioning of a structure may cause it to be treated as real property4. Thus if a thing is essential to the operation of a building, it may be real property even though it is not permanently attached. This is the test of adaptation. For example，keys to the house are considered realty under the test of adaptation.

The intention of the person attaching something to a structure may dertermine whether the thing is real or personal. If a landlord and a tenant agree that a built-in-dish-washer installed by the tenant can be removed at the end of the lease, then，with respect to the two parties, it will be treated as personalty. Without such an agreement, the built-in-dishwasher would be treated as realty.

If a thing, like a built-in store，that was once persona! becomes real property, we call it a fixture. The fixtures attached by business tenants are called trade fixtures. They are treated not as realty, but as personalty, because the courts presume the parties intend that they are not permanently attached.

Intellectual property is intangible and is often created and defined by law. Patents, trade secrets, copyrights and trademarks all fall in this category. A patent protects invention. TraHe secrets are items of information such as customer lists, formulae, and even recipes, tha. ;ire useful to a business and kept secret by the business. A copyright protects original works, such as books, advertisements, musical works and radio or television shows. A trademark is a name used to distinguish some goods from others.