Het gebruik van Mc is afkomstig uit Schotland & Ierland en het betekent "zoon van". De zoon van iemand met de naam Cartney kreeg dus de achternaam McCartney.
Een uitleg in het engels:
"Scottish and Irish patronymic surnames frequently have the prefix Mac or Mc. When these surnames were originally developed, they were formed by adding the Gaelic word mac, which means son of, to the name of the original bearer's father. For example, the surname MacDougall literally means son of Dougal. In later times, these prefixes were also added to the occupation or nickname of the bearer's father. For example, MacWard means son of the bard and MacDowell means son of the black stranger. "