-able vs -ible: The 5-Minute Rule That Ends the Guesswork
Comfortable but possible. Reliable but visible. Two endings, one sound, and a lifetime of guesswork until you learn the rule hiding underneath.
1. The core rule
Look at the word without the ending. If what's left is a complete English word, use -able. If it's a broken fragment, use -ible.
-able: the root stands alone
- comfort + able = comfortable
- rely → reli + able = reliable
- enjoy + able = enjoyable
- read + able = readable
- drink + able = drinkable
-ible: the root is a fragment
- poss… + ible = possible
- vis… + ible = visible
- horr… + ible = horrible
- terr… + ible = terrible
- flex… + ible = flexible
Memory trick: "If the word can stand alone, it's able to take -able. If it can't, it's a frag-ible."
2. Sound signals
When you can't see the root, listen to the letter before the ending:
- After a soft "c" (as in "ss") or a soft "g" (as in "j"), it's almost always -ible: possible, accessible, intelligible, suggestible.
- After a hard "c" or "g" (like "k" and "g" in "go"), it's almost always -able: practical, despicable, navigable.
3. The exceptions (there are few)
Every rule in English carries a small suitcase of exceptions. The -ible ones to memorize:
- sensible
- responsible
- possible
- incredible
- visible
- horrible
- terrible
- flexible
- digestible
- resistible
And the famous -able exception: capable, the fragment "cap" does exist as a word, so it plays by the rule.
4. Your quick checklist
- Drop the ending. Complete word left? → -able.
- Fragment left? Listen for soft c/g → -ible.
- Still stuck? The 10 exceptions above cover ~95% of the trickiest words. Commit those and you're done.
Final trick: "able" has a full word inside it: A-B-L-E, so the full word gets the full ending. Fragments get the skinny one.
Practice makes it permanent
Rules are easy to read and hard to remember. DrillUp drills the -able vs -ible category in five-minute daily challenges, with a memory tip on every word.
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