-able vs. -ible

Both are suffixes used to connote “can be”, “able to”, and “capable of”.  They are both added to words to give those words “power to be”, “ability to”, or “skill”. They are used to form adjectives when attached at end of words. The difference between the two is in when to use them.

 General rule of thumb:

The use of “Able”: if root word is a complete English word on its own. 

Examples: fashionable, affordable, valuable, suitable, comfortable, dependable.

The use of “ible”:  if the root word is not a complete functional word that can stand on its own.

Examples: audible, visible, horrible, terrible, edible, eligible, incredible, permissible.

Extra rule of thumb:

If the root is a complete word that ends in vowel, drop the last e, add –able.

Example: excus-e + able = excusable. Others: advisable, desirable, valuable, debatable.

If a word has a vowel before a y, keep the y and add –able. Example: enjo-y + able= enjoyable

If a word has consonant before y, drop y and add-ible. Example: rel-y + ible = reliable

Exceptions to the rules

The use of both –ible and –able for a single word which can either have the same meaning or carry different meanings. Examples: extendable vs. extendible, collectable vs. collectibles, defendable vs. defensible.

The use of –ible in complete words. Examples: contemptible, digestible, and flexible.

The use of –able in non-words. Examples: irritable, inevitable.

Take home lesson:

These rules may seem intuitive for Native English speakers, but it can be quite a challenge for those whose primary language is not English.  To make simplify things, use –able for complete words and –ible for non-words. Most words end with the suffix –able. Only about 76 English words have been identified as ending with suffix –ible.  So then, it is safe to say, when in doubt, use –able.

 

“Simplicity is the ultimate form of sophistication” –Leonardo De Vinci.