I would like to know if there is a rule when to pronounce ah in RP versus ae in GA. Is it a question of vocabulary or is there a rule for that?

Examples: dance- in RP is pronounced ah but in GA it is pronounced ae

or: can't, romance, cast, fast, etc.

  • The difference between RP and GA is that RP has the bath-trap split (answered in the second duplicate) – Mitch Jun 27 '16 at 18:45
  • It's not that simple. RP speakers pronounce 'stand' with a short A [it's a native word] but 'command' with a long A [it's borrowed from French, so pronounced in a kind-of-French way. Having said that, RP generally pronounces 'answer' with a long A although it's definitely of OE origin, but this morning I heard George Osborne [UK Chancellor of the Exchequer and undoubtedly posh] say it with a short A. So the rule is, there's no rule. – David Garner Jun 28 '16 at 8:36