Spelling Rules – double consonants
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thinner or thiner?
When to double a consonant before adding -er or -est
We add -er to a short adjective to form its comparative, and -est to form its superlative. We sometimes
double the final letter of the adjective when we do this:
 big ⇒ bigger, biggest,
biger
bigest
Sometimes, however, we don’t double the final letter:
 cheap ⇒ cheaper, cheapest,
cheapper
cheappest
This is the rule:
Comparatives and superlatives:
when to double a consonant before adding -er and -est

When forming a comparative or superlative form, we double the final letter of a one-syllable
adjective ending in consonant + vowel + consonant:
o big » bigger, biggest,
o fat » fatter, fattest,
o thin » thinner, thinnest

We don't double the final letter when the adjective ends in -y or -w:
o
o

grey » greyer, greyest,
slow » slower, slowest
We don't double the final letter when the adjective ends in
o
o
vowel + vowel + consonant
- cheap » cheaper, cheapest
or
vowel + consonant + consonant: - old » older, oldest
Spelling: when to double a consonant before adding -ed or -ing to a verb
We add -ing to a verb to form its present participle, and -ed to regular verbs to form the past simple. When
doing this, we sometimes double the last letter of the verb, as in these examples:

stop ⇒ stopped, stopping
stoped / stoping

refer ⇒ referred, referring
refered / referring
Sometimes, however, we don’t double the last letter, as with the verb visit:
 visit ⇒ visited, visiting
visited / visiting
Here’s the rule:
When to double a consonant before adding -ed and -ing to a verb
We double the final letter when a one-syllable
verb ends in consonant + vowel + consonant.*
stop, rob, sit
stopping, stopped,
robbing, robbed, sitting
We double the final letter when a word has more
than one syllable, and when the final syllable is
stressed in speech.
beGIN, preFER
beginning, preferring,
preferred
If the final syllable is not stressed, we do not
double the final letter.
LISten, HAPpen
listening, listened,
happening, happened
In British English, travel and cancel are exceptions to this rule:
travel, travelling, travelled; cancel, cancelling, cancelled.
* We do not double the final letter when a word ends in two consonants (-rt, -rn, etc.):
start – starting, started; burn - burn, burned.
* We do not double the final letter when two vowels come directly before it:
remain – remaining, remained.
* We do not double w or y at the end of words:
play – playing, played; snow - snowing, snowed.
Spelling: -ly endings of adverbs
Forming an adverb from an adjective is not usually a problem – we simply add ‘ly’:
slow becomes slowly, quick becomes quickly, etc.
Adjectives ending in –e, –le and –l, however, can cause problems.
Here are some simple rules:
When an adjective ends in -e, we simply add ly to form the adverb:

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polite
definite
absolute
complete
politely
definitely
absolutely
completely
Be careful when an adjective ends in -le. We remove the e and add y to form the adverb:


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probable
possible
terrible
reasonable
probably
possibly
terribly
reasonably
Don't be confused by adjectives that end in -l. Simply add ly and the adverb will then end in -lly:

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

hopeful
beautiful
helpful
careful
hopefully
beautifully
helpfully
carefully