Originally Posted by Deliverance
I thought Major and above were entitled to use that rank as their titles when they retired. Someone learned like Archimedes would surely know.
I think you meant 'Someone learned
or failing that, Archimedes', but I'll give it a shot.
The custom is for those of the rank of Captain and above (and RAF and RN eqivalents) to be allowed to employ their former ranks. ISTR a discussion here some years ago as to whether it was bad form for someone to insist on being called 'Flight Lieutenant Binky Volewarbler' when he was a Flt Lt retired. The conclusion was that a) yes he was and b) he was nevertheless a bit of a t!t for so doing.
Debretts has it that:
Field Marshals remain on the active list for life and so continue to use this rank. Other regular officers of the rank of captain and above may use, and be addressed by, their rank after being placed on the retired list.
The word 'retired' (abbreviated to 'Retd') should not be added after an officer's name in ordinary correspondence or in lists, but only when it is specifically necessary to indicate that an officer is on the retired list, eg, one employed in a civilian capacity in a Ministry of Defence establishment, when it facilitates postal arrangements.'
While I see jayteeto's point, Debrett's suggests that it is usually bad form to use the rank of Captain (or equivalent) on retirement if not being employed in a civilian capacity. Captain Mark Philips is an exception to this, since the origins of it being used came from the press, who referred to him as 'Captain Mark Philips' when he was competing in the 3 Day eventing team. When he was engaged to Princess Anne, the press continued to refer to him as 'Captain Mark Philips'. I believe that he never sought to use the title himself, and referred (and still does?) to himself simply as 'Mark Philips'.
Finally, given that the two most famous civilian Captains are Captains Peacock (are you free, mr Humphries?) and Captain Mainwearing, I'm not sure that it would necessarily be wise for the rank to be used, since it might well be ridiculed... And using rank might be a bad idea now Al-Qa'eda wannabes have attempted to target members of the armed forces (viz the recent case involving a plot against a chap awarded the CGC for his efforts in places sandy), and are probably likely to do so again - not necessarily making the distinction between serving and retired.