Courtesy titleIn the British peerage system, wives, children, and other close relatives of a peer are addressed by styless that may mislead those unacquainted with the system into thinking that they have substantive titles.
If a peer of the rank of Earl, Marquess, or Duke has more than one title, his eldest son uses one of the lesser titles. (The eldest sons of Barons and Viscounts do not recieve such a privilege.) If that eldest son has an eldest son, and there are additional titles available, he too may use a lesser title. For example, the Duke of Norfolk is also the Earl of Arundel and Lord Maltravers, and so his son may be styled Earl of Arundel, and the grandson styled Lord Maltravers. However, only the grandfather is a peer: the other two remain 'commoners' until they actually acquire a substantive title. Also, such courtesy titles are only used by the peer's eldest son, and the eldest son's eldest son, and so forth. Other descendants are not permitted to use the peer's subsidiary titles.
The actual title used is a matter of family tradition; it is usually chosen to avoid confusion with other peerage title. For instance, the Duke of Wellington is also the Marquess of Wellington and the Marquess Duoro. The Duke's son does not become the Marquess of Wellington (which could potentially cause confusion between the son and the father), instead becoming the Marquess Duoro.
A peer's wife takes her courtesy title based on her husband's rank, unless she herself has a higher title. Thus a baron's wife is called "baroness", an earl's wife is called a "countess", a duke's wife a "duchess", etc. Despite being referred to as a "peeress", she does not, however, become a peer "in her own right": these are 'styles', not substantive titles.
Another form of courtesy title, in the form of an honorific prefix, is granted to younger sons, and all daughters of peers. The rules differ for different ranks of peers: the children of a baron, for example, get the prefix "Hon.", the daughters of an earl are called "Lady", and so on:
|Peer||Wife||Eldest Son||Younger Son||Unmarried Daughter|
|Duke||Duchess||Father's Subsidiary Title||Lord [Firstname] [Lastname]||Lady [Firstname] [Lastname]|
|Marquess||Marchioness||Father's Subsidiary Title||Lord [Firstname] [Lastname]||Lady [Firstname] [Lastname]|
|Earl||Countess||Father's Subsidiary Title||The Honourable [Firstname] [Lastname]||Lady [Firstname] [Lastname]|
|Viscount||Viscountess||The Honourable [Firstname] [Lastname]||The Honourable [Firstname] [Lastname]||The Honourable [Firstname] [Lastname]|
|Baron||Baroness||The Honourable [Firstname] [Lastname]||The Honourable [Firstname] [Lastname]||The Honourable [Firstname] [Lastname]|
Note that a peer's daughter that marries a commoner retains her courtesy title (substituting her husband's surname for the maiden name), but if she marries a peer, she gains the courtesy title as that peer's wife. Also note that when the children of a peeress in her own right (a peeress that holds a substantive title) gain courtesy titles as usual, but the husband recieves no special distinction.