The Spelling Rules for Adding Suffixes:
When to double a letter.

To understand the doubling rule, it helps to know about vowel and consonant patterns in words.

One way to make a vowel sound long is to put e on the end:

tap, tape

bit, bite

cod, code

tub, tube

In two-syllable words, the first vowel is usually long if there is only one consonant between it and the next vowel:

paper

even

pilot

robot

music

The first vowel is short if there are two consonants between it and the
next vowel:

magnet

kennel

victim

bottom

butter

Some more examples:

fatter
later

better
Peter

dinner
diner

rocket
broken

supper
super

If you are unsure of these vowel and consonant patterns, look at Unit 8.

On page 1 of this unit, you learnt that there are two kinds of suffixes:

Vowel suffixes

ing	es	ed	er
en	est	ish	y
able	ible	al	ous

Consonant suffixes

less

ful

ness

ment

THE DOUBLING RULE:
If you add a vowel suffix to a short vowel word which has only one consonant at the end, you must double the consonant. If you don't, the vowel sound will change to a long one.

Click on the ear to hear these examples:

	Right	Wrong
stop + ed	stopped	stoped
dig + ing	digging	diging
fat + er	fatter	fater

To help you remember this rule, think of the second vowel as an invader. He is trying to attack the first vowel and make it change its ways. If he can get near enough, he will make it say its long sound.
Here, there is a strong wall of two consonants. This will protect the short vowel from attack. The invader can't get close, so the first vowel can carry on as before.

Now try these. Add the vowel suffix to the root word and type the answer.
Remember, y on the end is a vowel.
The first one has been done for you.

Add the suffix to the root word	Type the answer
swim + ing
shop + ing
hop + ed
flip + er
thin + est
rot + en
grub + y
clap + ing
red + ish
drum + er
mud + y
whip + ed