The General American dialect certainly has its own rules and idiosyncrasies.  That said, in dialect study, it’s inevitably compared to RP (Received Pronunciation or British English) since the language – English – is the same. 

Non-British non-Americans who wish to learn GenAm or RP will come to note how the two dialects differs from their own accent while speaking English and they begin the substitution or adjustment process of the various sounds to learn these new dialects.

Some words, though, in the pursuit of a target dialect simply don’t conform to the grander, overarching rules.  I’ve come to call these standalone considerations by the nickname “Rogue Words”.  Officially:  a word pronounced distinctly in a dialect (as compared to other dialects, or as compared to similarly constructed words) that doesn’t have a grander, over-arching rule governing its pronunciation.

My clients are provided with a detailed compiled list of these words quarterly.  I’ve included a few fun ones in this installment of my contribution to the Voiceover Community as a sample.  A huge acknowledgement must go to my cherished client roster who invariably knock over the rocks under which we find these gems. 

(It should be noted, when reading these, that my ear is tuned to the sounds of my coastal United States upbringing, to the fact that I am of European descent — Italian and Irish if you’re curious (though the dialects/accents that come to mind when you think of those ethnicities were not sounds I heard much of growing up) — and I am Caucasian.  It should be further noted that, as with all speakers of dialects, there can be many exceptions to all of these.)  

Try saying these out loud and see if you think you know why they’re on the list. 

General American:

• perfectly
• valuable
• been
• tumultuous
• pajamas
• sculpture 

Received Pronunciation: 

• been
• schedule
• aluminum (aluminium)
• McDonald’s
• maverick
• diagnose

– Tom Antonellis