Linguistics
The most common vowel sound in English isn't A, E, I, O or U
It's schwa, the flat 'uh' sound at the start of 'about' or the end of 'sofa.' English vowels lose their distinct quality when unstressed and collapse toward this same neutral, mid-central sound, so schwa turns up more often in ordinary speech than any single 'proper' vowel — despite having no letter of its own in the alphabet.