u/apricotical

This counts for the other senses as well:

Hypoesthesians=Hard of feeling

Aguesians=Hard of tasting

Anosmics=Hard of smelling

source: https://spaceplace.nasa.gov/all-about-venus/en/

I generally understood that you use “A” when the following word begins with a consonant. For instance, “A dog, a clock and a theme.”

The inverse is then true also. “An” precedes words that begin with a vowel. For example, “An extrovert, an isle, and an avocado.”

This makes perfect sense to me, but I struggle to understand why there are exceptions to this rule.

“An hour,” breaks the rule, as “An” precedes a word beginning with a consonant.

“A useless fact,” breaks the rule, as “A” precedes a vowel.

Both of these two examples would obviously sound awkward and wrong if they were spoken/ written following the same rule as most. “He had an useless fact he told me a hour ago.” Clearly improper and ill-sounding, but why?

Regarding the example of “An hour,” I thought that maybe since “hour” begins with a soft sound that doesn’t utilize the tongue touching the roof of the mouth it justifies the use of “An” since that is how words beginning with a vowel are spoken too[see the words “apple” versus “twister” as examples of what I’m trying to articulate]… but that can’t be it. Take the example, “A whirling tornado,” and note how “whirl” also begins with a consonant, but also with a soft sound that doesn’t require you to touch the roof of your mouth with the tongue, just like “hour.”

I don’t understand the exceptions, and why they are this way. I’m a native English speaker, just for further clarification.