Although English spelling rules have so many exceptions, there are some patterns that will help you with both your Spelling AND Pronunciation.
In this lesson you’ll some spelling rules for words ending in ‘-able’ or ‘-ible’.
Scroll down for practice with examples that you can use in the IELTS Test and my Complete Guide to Word Formation for IELTS.
1. Words ending in -able: a simple rule
Look at these common words ending in ‘able’ and ‘ible’. What do you notice about the ‘root’ word (the part before the ending) in each example?
e.g. comfortable: root word = ‘comfort’
‘-able’
acceptable
avoidable
considerable
doable
enjoyable
fashionable
predictable
preventable
questionable
reasonable
remarkable
sustainable
unthinkable
‘-ible’
audible
compatible
credible
edible
eligible
feasible
horrible
invincible
legible
negligible
possible
terrible
visible
Words which end in ‘-able’ have a recognisable ‘root’ word at the start.
‘-able’ words usually come from French and ‘-able’ is a ‘living’ suffix, meaning that it is still being used to create new words e.g.
- ‘That name is unpronounceable!’ (unable to be pronounced)
- ‘Everything is figureoutable’ (everything can be figured out)
- ‘I’m sure it’s fixable’ (able to be fixed)
When a word ends in -ible, the part before the ending is not usually a recognizable English word e.g. ‘terrible‘ or ‘horrible‘ come from ‘terror’ and ‘horror’ but ‘terr-‘ and ‘horr-‘ are not recognisable English words.
‘-ible’ is only used in older (Latin) words that have survived into modern English.
2. How to remember the difference
The above rule is a useful one, though there are exceptions (see #3 below).
There are about 900 words ending in ‘-able’ and only about 200 ending in ‘-ible’ so if you had to guess e.g. in the Listening gapfill test, it might be safer to choose ‘-able’.
Otherwise you just have to learn individual words. In this lesson I am only using the ones which I think will be useful for you in the IELTS Test, so you don’t have to learn them all! (scroll down for full list).
3. Words ending in -ible: exceptions
As you know, there are exceptions to EVERY rule in English.
For example, access/ible ends in -ible even though it is formed from a recognisable root word (access).
Also:
- convert→convertible
- corrupt→corruptible
- destruct→destructible
- flex→flexible
- resist→ (ir)resistible
Here are some common ‘-able’ words which have no recognisable root form but still take ‘-able’.
- applicable
- available
- durable
- hospitable
- inevitable
- probable
- vulnerable
- viable
4. Words ending in - able: spelling rules
1. What happens when you add -able to these verbs?
a) argue, breathe, debate, inflate, translate, value
b) notice, replace
a) Omit the final ‘e’ from the root verb:
- arguable, breathable, debatable, inflatable , translatable, valuable
b) Don’t omit the final ‘e’ from the root verb:
- noticeable, (ir)replaceable
2. What happens when you add -able to these verbs?
- forget, program, stop, transfer
Double the final letter:
- forget→(un)forgettable
- program→progammable
- stop→(un)stoppable
- transfer→transferrable
3. How do you change these verbs to ‘-able’ adjectives?
- demonstrate
- navigate
- negotiate
- operate
- penetrate
These are all irregular – drop the ‘ate’:
- demonstrate → demonstrable
- navigate → navigable
- negotiate → negotiable
- operate → (in)operable
- penetrate → (im)penetrable
4. How do you change these verbs to ‘-able’ adjectives?
- deny
- envy
- justify
- rely
- vary
Change the ‘y’ to ‘i’:
- deny→deniable
- envy→enviable
- justify→justifiable
- rely→reliable
- vary→variable
6. Practice
Test yourself with these IELTS-related sentences (the quiz usually works better on Desktop).
All of the words are taken from this page.
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