The correct one is "An hour", both for speaking and writing.
A good rule of thumb is that any words that starts with a vowel - a,e,I,o,u - gets 'an'. But it really more matters about the sound. Basically, in this case the h is silent in hour. Such is the case in alot of similar words - heir, honest, hourglass. Because the h is silent, you're starting with an O, which is a vowel. But take X-Ray for example. When you say it, the first sound said is 'Ex', and that starts with a vowel, so it's 'an X-ray.
That's the gist of it. It really depends on the sound rather than the word that begins. Really do hope that helps. |