And the Gileadites took the passages of Jordan before the Ephraimites: and it was so, that when those Ephraimites which were escaped said, Let me go over; that the men of Gilead said unto him, Art thou an Ephraimite? If he said, Nay;
Then said they unto him, Say now Shibboleth: and he said Sibboleth: for he could not frame to pronounce it right. Then they took him, and slew him at the passages of Jordan: and there fell at that time of the Ephraimites forty and two thousand. (Judges 12:5-6)From this, a shibboleth has come to mean "any distinguishing practice that is indicative of one's social or regional origin...it usually refers to features of language." Wikipedia further notes that American soldiers used shibboleths in WWII, discovering enemy spies by using the word "lollapalooza" in the Pacific and a working knowledge of baseball in Europe. (This is how they discover the bad guy in a great scene from one of my favorite movies, Stalag 17.) On a side note, I would think that the "th" sound would be a major distinguishing sound for native English speakers.
Anyway, I went home and was contemplating language and shibboleths when I came across an article which states that the assumption that British and American accents diverged after the Revolutionary War is largely accurate, but it was British who changed! In essence, most everyone used to speak in what we would identify today as the American accent, but in the early 1800s the British aristocracy developed a "more refined" manner of speaking. The upper class took on a non-rhotic accent--meaning that they don't pronounce their Rs--which was gradually adopted by most of England (but not Ireland or Scotland). Meanwhile, some of the parts of US more heavily influenced by the Brits (Bah-ston, pahts of the South) also dropped their Rs. Crazy, huh?
But most importantly, all those knocks on Kevin Costner's Robin Hood not having a British accent are ill-founded.