The Complete List of
English Spelling Rules

Lesson 16: -able or -ible

In this series of lessons, you will learn useful spelling rules in English.

This lesson will provide guidelines on adding the suffixes -able and -ible. They have the same meaning, so it is important to know when you should use each one.


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As we have seen in a previous lesson, a suffix is an ending that can be added to a word. The suffixes -able and -ible both create adjectives, and they mean "can be done."

Choosing -able or -ible depends on the word the suffix is being added to. The suffix -able is more common. Here are some rules to help you know which to use.

-able

1. When the base word before the suffix is a complete word

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In the sentence above, "fashionable" means stylish. The part of the word before the suffix -able is a complete, recognizable word: fashion.

In cases like this, you will use -able and not -ible.

Notice that words that end in -ce and -ge keep their final -e before adding -able. There are also a few important exceptions that keep their final -e, which you should memorize: sizeable, likeable, nameable.

Here are some examples:

• noticeable
• changeable
• manageable
• laughable
• transferable
• preferable
• suitable
• impressionable
• adaptable
• likeable
• peaceable
• knowledgeable
• comfortable
• washable
• affordable
• sizeable
• likeable
• nameable

2. When the base word ends in an -e that is eliminated

Often, base words that end in -e need to have that final -e eliminated before adding -able. When this happens, you should use -able and not -ible.

As we saw above, base words that end in -ce and -ge keep their final -e before adding -able.

Here are some common examples:

• debatable
• pleasurable
• adorable
• desirable
• measurable
• conceivable
• excusable
• excitable
• disposable

3. When the last consonant of the base word must be doubled or the final -y must be changed to an -i

When the base word ends ing a single vowel and a single consonant, and the emphasis is on the last syllable of the word, that final consonant must be doubled before adding the suffix -able. For more on this, you can check our lessons on adding -ing or adding -ed.

Also, when the base word ends in a consonant and a -y, that -y must be changed to an i before adding -able.

In these cases, you should use -able and not -ible.

For example:

• forgettable
• justifiable
• reliable
• regrettable
  
  

-ible

Finally, in general when the base word is not a complete and recognizable word, you should use -ible. However, this is not a strict rule. It is important to be careful using -ible.

You will see that many base words end in -t before the -ible is added. You can look for this pattern. Also, you will never see a final -e before -ible.

Here are some common words with -ible:

• terrible
• horrible
• visible
• responsible
• invincible
• accessible
• sensible
• incredible
• illegible
• eligible
• convertible
• suggestible
• digestible

Review

So, let's review what we have learned about the suffixes -able and -ible in English:

1. When the base word is a complete and recognizable word, you will usually use -able.
   
   
2. When the base word ends in -e, you should remove then -e, then add -able. Leave the -e when the word ends in -ce or -ge.
   
   
3. If you must double the final consonant of the base word or change the final -y to i, add -able.
   
   
4. In general, -ible is less common and the base word is not a complete and recognizable word. However, there are some exceptions.

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