Peerage of England
The ranks of the English peerage are, in descending order, Duke, Marquess, Earl, Viscount, and Baron. While most newer English peerages descend only in the male line, many of the older ones (particularly older baronies) can descend through females. Under English inheritance law all daughters are co-heirs, so many older English peerage titles have fallen into abeyance between various female co-heirs.
Courtesy titles in the United Kingdom
If a peer of one of the top three ranks of the peerage (a duke, marquess or earl) has more than one title, his eldest son - himself not a peer - may use one of his father's lesser titles "by courtesy". However, the father continues to be the substantive holder of the peerage title, and the son is only using the title by courtesy, unless issued a writ of acceleration. If the eldest son of a duke or marquess has an eldest son, he may use a still lower title, if one exists. In legal documents the courtesy title is implied but not used directly, e.g. the name of the person is given then "commonly called [title]".