A royal family typically includes the spouse of the reigning monarch, surviving spouses of a deceased monarch, the children, grandchildren, brothers, sisters, and paternal cousins of the reigning monarch, as well as their spouses. In some cases, royal family membership may extend to great grandchildren and more distant descendants of a monarch. In certain monarchies where voluntary abdication is the norm, such as the Netherlands, a royal family may also include one or more former monarchs. In certain instances, such as in Canada, the royal family is defined by who holds the styles Majesty and Royal Highness. There is often a distinction between persons of the blood royal and those that marry into the royal family. Under most systems, only persons in the first category are dynasts, that is, potential successors to the throne (unless the member of the latter category is also in line to the throne in their own right, a frequent occurrence in royal families which frequently intermarry). This is not always observed; some monarchies have operated by the principle of jure uxoris.