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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.

a happy woman throwing papers

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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

a lady in a formal dress and gloves

Years ago, it was fashionable for ladies to wear gloves at formal events.

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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

a woman watching a movie

Lily did not like the movie because it was not very believable.

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

a woman at her birthday party

Kelly's surprise party was really unforgettable for her.

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

a woman dancing

Dancing is a great way to stay flexible and healthy.

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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