:I think all the Spanish dukedom articles are now "Dukes of Foo". See Category:Dukedoms of Spain. To me, "Duke of Foo" implies an article about an individual. "Duchy" implies a territorial domain, while "dukedom" implies that there is no such domain. I thought that "dukes" would allow me to put all these articles at accurate names without my having research each case separately. If you know which are which, I'm fine with "Dukedom of Foo."