A/an before a word is dependant on how the subsequent word is pronounced, not spelled. So for that sentence, the implication is that it’s pronounced closer to “erb”, thus “an” to precede instead of “a”. Another example that’s a bit counterintuitive is “one” being pronounced like “won”, so you’d get “a one time thing” rather than “an one time thing”.
A/an before a word is dependant on how the subsequent word is pronounced, not spelled. So for that sentence, the implication is that it’s pronounced closer to “erb”, thus “an” to precede instead of “a”. Another example that’s a bit counterintuitive is “one” being pronounced like “won”, so you’d get “a one time thing” rather than “an one time thing”.
I’m aware of when to use “a” versus “an”, but I wasn’t aware that Americans don’t pronounce the “h”! It makes a lot more sense now, thanks!
…well, a little bit more sense, anyway - I’m still not sure what calling someone “a herb” actually means…