A  sept  may be described  as  a family
group   or  a   small  clan  which,  f or
protection, has allied itself to a larger
(and stronger) clan  pledging, to come
to the  assistance of  the  larger clan in
time  of  need.   The  late Chief, James
MacArthur,     instructed    that     the
MacArthurs had no septs though some
publications,  such  as   “Scots  Kith &
Kin,” list some.   Clan  Campbell  and
Clan MacDonald  are two clans which
list "MacArthur" as a sept.
 Following is a guide to some of the many variant spellings of the name MacArthur.  The old axiom that “Mac” names are Scotch and “Mc” names are Irish is totally false, as such prefixes can be found in both countries.  Where long lists of names of Scots were tediously handwritten by scribes, the task was made easier by using an apostrophe instead of the prefix, so such forms “M’Arthur” often were recorded.                              
It is possible some  of the names listed  are related  to MacCarthys of Southern Ireland,
MacArtans of Northern Ireland or even MacCartneys of unknown origin.  It  is equally
possible that MacCarthy, MacArtan and MacCartney are septs of Clan Arthur. For this
reason the  list may contain inaccuracies.  M' and  Mc  are abbreviations  of Mac. “The
Surnames  of  Scotland,” by George Fraser Black, may answer some questions relative
to names.