An 80% decrease ~ a 80% decrease

Question

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?

Usenet · Accepted Answer

[nq:1]I stumbled upon the latter use recently, and it got me thinking. There seems to be some exceptions to the ... ... Anyone have some fun or interesting examples in this exercise? Or some links for simplified rules on the matter?[/nq]
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

Usenet · Answer

[nq:1]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"...[/nq]
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

An 80% decrease ~ a 80% decrease

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