Here's why:
* Short vowels have a short, quick sound, like the "a" in "cat" or the "e" in "bed".
* Long vowels have a longer, drawn-out sound, like the "a" in "cake" or the "e" in "be".
In the word "fever", the vowel "e" is pronounced with a long "e" sound, similar to the "e" in "see". Therefore, it's a long vowel word.