First, I tried to simplify the titles to that of the British system, for example, Somdetch Chao Praya would be a Duke, Chao Praya would be a Marquis, Praya is an Earl, and so on. But, it turns out to be completely different, no relationship to each other whatsoever. So, the titles must then be understood as they are in the Thai context. The rankings of the titles are as follows, with 6 being the first title one is normally given, and then work up to 1, the highest rank to have been given to ordinary citizens of Siam..
“Kun” was the first title one would normally receive. In old Siam , one would normally get bestow a title for being a good and hard-working civil servant. Non-civil servants, namely important people in the trade sector, were qualified for the titles if they have achieved good deeds in the eyes of the King. The rank of “Chao Praya” was quite rare enough, and would normally go to civil servants, as well as those who worked directly for the King, and the Royal Family. “Somdetch Chao Praya” was even rarer, and was bestowed upon direct servants of the King, for example, Somdetch Chao Praya Borom Maha Sri Suriyawongse from the Bunnag family was given this title because he was at one time Regent to the Kingdom, during a transition period between the reigns of Kings Rama IV and Rama V, when King Rama V was still too young to rule. These titles were not just prestigious for the family, but brought also regalias for the titles, mostly made in gold and precious stones, as well as vast amount of land, much like the British system.
Once the men get one of these titles, their wives will also use them as surnames. For example, Chao Praya Sripipat Ratana Raja Kosa Thibodi's wife was styled Khunying Prapai Sripipat Ratana Raja Kosa Thibodi.
There are two aristocratic titles for women,
Since the end of absolute monarchy, the male titles were abolished, but those who have received titles before the abolishment were able to enjoy the use of their titles until their death. Oddly enough, the titles for women remain to this day, and many look forward to 5 May of every year when HM the King bestows these titles and upgrades to the ladies. The titles for women could possibly be compared to the British Dames, though many of the ladies try to use the British equivalent of Lady which is rather at odds with their long Thai names, and so is not quite in common use of late. The title of Khunying is a bit confusing these days, as the Mom Rajawongses are styled Khun Chai (for men) and Khun Ying (for women), when addressing them informally. Thus, one would have to have the knowledge of who is a Khunying by birth, i.e. Mom Rajawongse, and who is a Khunying given. There are also confusions in the use of the title, if one already has a title. The clarifications are as follows:
The title of Mom Chao is above all given ranks, so the receiver will continue to style herself HSH Princess. The Than Ying is an informal form of addressing a princess (Mom Chao), and when she marries a commoner (including those with titles below her - M.R. and M.L.) she will lose her title, thus she has to use the given title of Khunying or Thanpuying. A Mom Rajawongse is above a Khunying but below a Thanpuying, so she will still style herself a Mom Rajawongse if she receives a Khunying, but uses the Thanpuying once given. The Mom Luang is below a Khunying, so once she receives that title, she has to use it, and forget about the Mom Luang. An unmarried person will style herself Khun when given both titles.