Adding the suffixes -able and -ible:
do the root words change?

-able and -ible are suffixes which change verbs to adjectives.

Follow the rules you know for adding a vowel suffixes.

(To review the suffixing rules, go to Unit 9)

Teaching point 1. If the syllable just before the suffix -able or -ible is the stressed syllable, you will be able to hear a clear short vowel in that syllable. Therefore you will usually need a 'wall' of two consonants to protect that short vowel. For example:
forget + able = forgettable
admit + ible = admissible

2. If the base word ends in e you can usually drop the e, because -able and
-ible both start with a vowel. For example:

excuse + able = excusable
sense + ible = sensible


difficult words, learn not to make mistakes Some root words end in :
-ce with the sound /s/
or -ge with the sound /j/

You need to make sure you do not lose these 'soft' sounds for c and g when you add a suffix. The vowels e, i and y make c say /s/ and g say /j/. The letter a will not do this job so, if the suffix is -able and the ending is -ce or -ge, you must keep the final e of the root word. For example:

service + able = serviceable
manage + able = manageable

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Test yourself on the suffix rules for -able and -ible.
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Unit 27: Spelling the endings -able and -ible

Page 8 of 11

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