A thing is private which is not common.

Explanation

(English-origin maxim.) Private property or right is defined by exclusion from common use — cite this to establish that a thing claimed as private cannot simultaneously be treated as public or common.

Where this applies

• A homeowner argues that her backyard is private property because it is fenced, gated, and not open to the public, and the court agrees that what is excluded from common use is by definition private.
• A company's trade secrets are protected precisely because they are not shared with the public — the fact that the information is kept from common knowledge is what makes it private property.
• A landowner posts 'No Trespassing' signs and excludes the public from a wooded area on her property, and the court holds the land is private because it is not held in common use.