Spelling, here it comes around again. English is just one of those languages (not unlike French), where the spelling often has very little to do with the actual pronunciation of the word and where the few concrete rules that exist can be difficult to spot.

This short article tackles one of the trickiest issues: double letters.
When I say double letters, I don't mean the -tt- in butter, or the -pp- in appear, rather rules governing when the consonants at the end of words should be doubled before endings beginning with vowels, such as in begin - beginning as we have just seen. The most commonly found vowel endings are -able, -ed, -en, -er, -est, -ible, -ing, -ous.

Here are some handy hints in the form of a list.

The final consonant should be doubled for:

1. words with only one syllable and a short vowel, e.g.
   big - bigger, biggest; fit - fitted or again cut - cutting
   By the same token, there is no need to double when the vowel is long, such as in look - looking.
    
2. words with more than one syllable, where the stress falls on the final syllable, e.g. refer - referral, referred
   This rule is also useful for determining when you should not resort to doubling. Pronounce the word aloud to determine where the stress falls and your spell checker will never catch you out again for those common mistakes such as benefited, targeted.
   There are, of course, as with any language, exceptions to this rule, the best known being handicap, kidnap and worship which all require doubling at the end.

Consonants that are already double require no further doubling (!) and w, x and y at the end of words are never doubled, thus withdraw - withdrawing.

Some special rules exist for words ending in -l:

1. a single -l following a single vowel when written should always be doubled, regardless of the emphasis when saying the word out loud, e.g.:
   cancel - cancellation, fulfil - fulfilled.
   Thus all adjectives ending in -ful convert to adverbs ending -fully.
   Note that parallel - paralleled is an exception to this rule.
    
2. a single -l not preceded by a single vowel when written is not doubled, such as in
   fool - fooling or curl - curled
   Again we see common exceptions in wool - woollen and dial - dialling, dialled
    
3. endings that begin with a consonant have no effect on the single -l, e.g.:
   rival - rivalry, but rivalling, fulfil - fulfilment
   In the case of a final -y, the -l should be doubled:
   loyal - loyally with the exception of oil - oily

Differences do exist in this area between American and British English spellings. As a native Scot, I have based my advice on the British spelling system, but any good dictionary will always offer you both.