In all vowels, the mouth passage is unobstructed. If it is obstructed at any time during the production of a speech-sound, the resulting sound will be a consonant.” (Charles Laurence Barber, The English Language: A Historical Introduction. Cambridge Univ. Press, 2000)

“In written English, . . . the 26 letters of the alphabet comprise 5 vowels and 21 consonants. In spoken English, there are 20 vowels and 24 consonants. It is this discrepancy, of course, which underlies the complexity of English spelling.” (David Crystal, How Language Works. Overlook Press, 2006)