Page 585 - Practical English Usage 3ed - Michael Swan, Oxford

spelling (7): doubling final consonants 562
562 spelling (7): doubling final consonants
1 doubling before vowels
We sometimes double the final consonant of a word before adding -ed, -er, -est, -ing, -able, -y (or any other ending that begins with a vowel).
stop -+ stopped sit ..... sitting big..... bigger
2 Which consonants are doubled?
We double the following letters:
b: rub ..... rubbing
d: sad ..... sadder
g: big..... bigger
l: travel..... traveUing m:slim ..... slimming
n: win -+ winnable p: stop -+ stopped
r: prefer ..... preferred t: sit ..... sitting
We double final -s in gassing, gassed (but not usually in other words), final-z in quizzes. fezzes, and final-fin iffy (a colloquial word for 'questionable', 'uncertain').
Final w (in words like show, flow) is part of a vowel sound, and is not doubled.
show -+ showing; flow ..... flowed (NOT sh6wl#ing, jltJwwed)
3 only at the end of a word
We only double consonants that come at the end of a word. Compare: hop ..... hopping BUT hope ..... hoping
fat ..... fatter BUT late -+ later
plan ..... planned BUT phone ..... phoned
4 one consonant after one vowel letter
We only double when the word ends in one consonant after one vowel letter. Compare:
fat ..... fatter BUT fast ..... faster (NOT JY13ttef')
bet ..... betting BUT beat ..... beating (NOT beaning)
5 only stressed syllables
We only double consonants in stressed syllables. We do not double in longer words that end in unstressed syllables. Compare:
up'set ..... up'setting B U T be'gin ..... be'ginning B U T re'fer ..... re'ferring BUT
'visit ..... 'visiting 'open ..... 'opening
'offer ..... 'offering
Note the spelling of these words:
'gallop..... 'galloping..... 'galloped (NOT gaUtJ1'1'ing, gfll:lttppetl) de'velop ..... de'veloping ..... de'veloped (NOT tle/Jel8rJfJing. tleuel8fJfJetJ)
6 exception: final I in unstressed syllables
In British English, we double -l at the end of a word after one vowel letter, in most cases, even in unstressed syllables.
'travel ..... 'travelling
'equal ..... 'equalled
In American English, words like this are most often spelt with one l: traveling.
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