For years I had been teaching people that speakers of rhotic accents pronounce an r sound wherever there is a letter r in the spelling, and not where there isn’t. Non-rhotic speakers on the other hand — which includes me and most of the students I lectured to at UCL — don’t, since we have lost /r/ except before vowel sounds.
I would illustrate this with pairs such as court–caught, larva–lava, sore–saw, career–Korea, tuber–tuba, manner–manna, western–Weston — and dear–idea.
Then I started to notice that sometimes I would hear rhotic speakers who nevertheless seemed to be pronouncing r at the end of idea. How could this be? Anyhow, I had to start expressing myself rather less sweepingly, more circumspectly. Some words (not only colonel) seemed to be exceptions. They had no <r> but they did have [r] for some rhotic speakers. (See also my blog for 11 October 2007, and Accents of English vol. 2 p. 343.)
(We non-rhotics do sometimes say aɪˈdɪər, of course, but only before vowels: that’s our “intrusive r”, ðə ˈveri aɪˈdɪər əv ɪt. But that’s a quite different matter.)
Now the Scottish (and correspondingly rhotic) phonetician Jim Scobbie has revealed the shocking facts. He reports that he has an “extra” r in the items Chicago, unauthorised, theatre, idea and, as he has just noticed, in inaugural.
There is no historical r at the relevant point in these words. The explanation is presumably false analogy in words first heard pronounced by nonrhotic speakers. If a Scot hears an English person say ˈɔːɡən organ and knows that it corresponds to Scottish ˈɔrɡən, it’s entirely understandable that he would infer that for English English ɪnˈɔːɡjʊrəl the corresponding Scottish form must be ɪnˈɔrɡjərəl. Spelling doesn’t come into it.
In rhotic accents outside Britain, where the influence of England’s non-rhoticity is weaker — in America, in Canada, even in Ireland — you would expect this sort of thing to be less likely to happen.