Marquis and Marquess

One of the most respected and often referred to sources of how to address a member of the peerage is Laura chinet. Her website is here:

http://chinet.com/~laura/html/titles12.html

She gives a clear and exhaustive example of each of the titles and their families and how they were addressed. Since I cannot improve upon perfection, I won't try, so I'll simply pass along the source in case you struggle with it.

However, there has been some discussion as to whether it was correct by the Regency to use Marquess or Marquis. I prefer to use Marquis. It just looks better to me—maybe because it looks French. Debrett's 1802 version, and most of the  peerage books published at that time, use Marquis. Debrett lists the plural as Marquisses. However, by 1828, Debrett changed the spelling to Marquess. The change may have resulted to popular use as in the way dictionaries keep up with modern terms and meanings, or Debrett may have caused the change. I do not have an original statement as to the wording when Wellington was created a Marquess so do not know how it was spelled, but The Royal Kalendar of 1815 says Marquises.

Somewhere I read that  between 1816 and 1828, the Marquises in the Kingdom decided that they preferred the form of Marquess, probably because it sounded more English. After a long war with France, that was probably a subtle way of declaring their independence and perhaps a sigh of relief that Napoleon did not conquer them.