YSK: Use ‘a’ when the word starts with a consonant sound, and ‘an’ when it starts with a vowel sound
Why you should know: The ‘a’ vs ‘an’ conundrum is not about what letter actually begins the word, but instead about how the sound of the word starts.
For example, the ‘h’ in ‘hour’ is silent, so you would say ‘an hour’ and not ‘a hour’. A trickier example is Ukraine: because the ‘U’ is pronounced as ‘You’, and in this case the ‘y’ is a consonant, you would say “a Ukraine” and not “an Ukraine”.
I'm curious on what others' thoughts are on this: do you say/write "a history" or "an history"? I personally use "a history", but i've seen significant usage of "an history". Do people not pronounce the 'h' in "history"?