Here's how it works:
* The "e" at the end of the word is a silent "e". It's not pronounced, but it has a powerful impact on the vowel sound before it.
* Silent "e" rule: In many words, a silent "e" at the end of a word makes the vowel before it "long". This means the vowel sound is the same as the letter name, like "a" in "ate".
Therefore, the "a" in "great" is a long "a" sound, similar to the sound in "fate" or "bake".