A or An ???

When should we use a or an? This has been coming up in a lot of classes lately so I thought I would also talk about it here. The grammar rule states that an is used when the following word starts with a vowel: a, e, i, o, u. But an is used not only when the word starts with a vowel, but it is also used with words that sound like they begin with a vowel. For an example, look at the word hour, that would sound funny if you said a hour even though according to the rule, a is what you are taught to use. So if you are wondering which to use say the word out loud to see if it sounds right. An hour, or An honest person. Because they have a silent h they are used with an. I hope this helps! :)