The Grammarphobia Blog

Is it “-able” or “-ible”?

Q: Is there a rule for remembering the correct spellings of words ending in “-able” or “-ible”? You know, words like “portable,” “possible,” “manageable,” “delectable,” “suitable.” Hmm… Now I’m having trouble coming up with another “-ible.” Perhaps treating “able” as the norm and remembering the “-ible” exceptions will do it?

A: There’s no rule, exactly, for telling the “-ables” from the “-ibles.” Often a word derived from a Germanic source (Old Dutch, Old Icelandic, Old Norse, and so on) will end in “-able,” like “forgivable,” which comes from Old English.

If a word is derived directly from Latin, however, it might be spelled one way or the other. It generally will end in “-able” if the  original Latin verb ended in “-are.” And it will probably end in “-ible” if  the  original Latin verb ended in “-ere” or “-ire.” 

That accounts for English words like “legible,” from the Latin legere (“read”), “collectible,” from colligere (“gather”), and “potable,” from potare (“drink”).

There are exceptions, though. And not many of us know automatically whether a word is derived from Latin or Old English. Only one thing is certain: there are far more “-ables” than “-ibles.” The best rule to follow is this: When in doubt, look it up.

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