Peerage
Lord is used as a generic term to denote members of the peerage. Five ranks of peer exist in the United Kingdom, in descending order these are duke, marquess, earl, viscount, and baron. The appellation 'Lord' is used most often by barons who are rarely addressed by their formal and legal title of "Baron", a notable exception being during a baron's introduction into the House of Lords when he begins his oath by stating "I, Baron X...of Y...". The correct style is 'Lord (X)', for example, Alfred Tennyson, 1st Baron Tennyson, is commonly known as 'Lord Tennyson'. The ranks of marquess, earl and viscounts are commonly also addressed as lord. Dukes use the style 'Duke of (X)', and are not correctly referred to as 'Lord (X)'. Dukes are formally addressed as 'Your Grace', rather than 'My Lord'. In the Peerage of Scotland, the members of the lowest level of the peerage have the substantive title 'Lord of Parliament' rather than baron.
For senior members of the peerage, the appellation of lord is used as a courtesy title for some or all of their children; for example the younger sons of dukes and marquesses are entitled to use the style 'Lord (first name) (surname)'. The titles are courtesy titles, in that the holder is not deemed thereby to hold a peerage, and is a commoner, according to Law of the United Kingdom.
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