1. 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’
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. Learn these 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).
- resist→ (ir)resistible
Here are some common ‘-able’ words which have no recognisable root form but still take ‘-able’.
4. Some spelling rules
1. What happens when you add -able to these verbs?
a) argue, breathe, debate, inflate, translate, value
b) notice, replace
2. What happens when you add -able to these verbs?
- forget, program, stop, transfer
3. How do you change these verbs to ‘-able’ adjectives?
4. How do you change these verbs to ‘-able’ adjectives?
Test yourself with these IELTS-related sentences.
All of the words are taken from this page.
Get more help with IELTS grammar
Get more practice and a free booklet about word formation
How to use ‘despite’ and ‘in spite of’
How to use concession in Writing Task 2.
How to write complex sentences for IELTS.
Coherence and Cohesion for IELTS Task 2.
‘Not only but also’ and inversion
How to use ‘the former, the latter’
How to correct your grammar mistakes in IELTS
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