Consonants are the rest of the letters in the alphabet: b, c, d, f, g, h, j, k, l, m, n, p, q, r, s, t, v, w, x, y and z The letter 'y' is a bit different, because ...
The answer partly depends on whether we are talking about the sounds or letters of vowels and consonants. By mentioning “alphabetic languages”, the questioner is presumably asking why most versions of ...