Rules for superlatives

[RobNik]

Hi,

In a few places I have read that when forming the superlative adjective, words ending in consonant-vowel-consonant get the last consonant doubled. For example: big, biggest; flat, flattest. But here is an example that violates this rule: slow, slowest. So, my question is: does anyone know a better statement of the rule? Is it only certain consonants? Or maybe best to tell students it's simply a rule with some exceptions that they have to learn individually.

Rob

[5jj]

A single consonant letter representing a consonant sound following a single vowel letter is doubled.

'Slow' is not an exception, in that sounds represented by the letter w are not phonetically consonants. Phoneticians class /w/ as a glide or semi-vowel. It shares some of the characteristics of a consonant; for example, nouns beginning with /w/ follow a, not an. However, there is no consonantal obstruction of the airflow when /w/ is produced. The sound after /sl/ in 'slow' is a diphthong, /əʊ/ in BrE; there is not a trace of a consonant sound..

[RobNik]

Great answer, thanks.