I stumbled upon the latter use recently, and it got me thinking.
There seems to be some exceptions to the simple rule that I still
use when deciding on "a" or "an"...

If you go by the word "decrease", the "a 80% decrease" would be
correct, but should you really dismiss the preceding "eighty"?
Why? Because it's not a word, but a number?

I go by the first letter of the first word after the prefix.
Except for certain words, where the letter makes a "vocal
sound", instead of a "vowel sound". (What is the proper term
for this, incidentally?)

These are some examples of what I would use. Am I wrong anywhere?:

An 80% decrease
A 50% increase

A door
An office door

A herd
An herb (because the h is mute)

An orange
A yellow orange

A boat
An orange boat

... Anyone have some fun or interesting examples in this exercise?
Or some links for simplified rules on the matter?

"Thomas Hejl Pilgaard"  wrote...
>I stumbled upon the latter use recently, and it got me thinking.
> There seems to be some exceptions to the simple rule that I still
> use when deciding on "a" or "an"...
>
> If you go by the word "decrease", the "a 80% decrease" would be
> correct, but should you really dismiss the preceding "eighty"?
> Why? Because it's not a word, but a number?
>
> I go by the first letter of the first word after the prefix.
> Except for certain words, where the letter makes a "vocal
> sound", instead of a "vowel sound". (What is the proper term
> for this, incidentally?)
>
> These are some examples of what I would use. Am I wrong anywhere?:
>
> An 80% decrease
> A 50% increase
>
> A door
> An office door
>
> A herd
> An herb (because the h is mute)
>
> An orange
> A yellow orange
>
> A boat
> An orange boat
>
> ... Anyone have some fun or interesting examples in this exercise?
> Or some links for simplified rules on the matter?

You're right with all these.  However, the 'h' in 'herb' is NOT mute in 
UK English so in that context you would say "a herb".

A rule often followed in the case of a word beginning with 'h' is that 
the letter is mute if the first syllable is unstressed.  Those who 
follow this rule would say "a history..." but "an historical ...";  "a 
hospital" but "an hotel".

Matti

Thomas Hejl Pilgaard wrote:
> I stumbled upon the latter use recently, and it got me thinking.
> There seems to be some exceptions to the simple rule that I still
> use when deciding on "a" or "an"...
> 

Don't make it too complicated! It goes almost entirely by the results 
when spoken. "an 80" could just as easily be written "an eighty". The 
mute h is fairly rare nowadays, both spoken and written, and "an hotel" 
would usually be considered "lah-di-dah", affectedly upper-class. 
"Honour" in UK English stuill has the silent H, so you would say "It's 
an (h)onour to be a hostess in a hotel". "a/an" NEVER takes its form 
from ANY word but the one after it.

Honour, honesty, heir, hour- I can't think offhand of any other words 
that have the silent initial H nowadays.

Beware of the letter U. In UK English this can have a vowel sound or a 
consonantal sound- "oo" or "you". There is some disagreement over 
this... some would say "a unique value" ("a younique"), others (rarer) 
"an unique.." ("an younique.."), though those same people would never 
say "an young man".

It also goes by pronunciation with acronyms- you would say "I've bought 
an FT", but "I've bought a Financial Times" and "Here's the PO", but 
"Here's the purchase order".

JS