-able and -ible
The suffix -able, as in readable, is far more common than -ible, as in audible. (Both are pronounced the same: /əbl/). Some common words spelt with -ible:
- accessible
- audible
- comprehensible
- convertible
- credible
- defensible
- digestible
- divisible
- edible
- eligible
- exhaustible
- fallible
- feasible
- flexible
- forcible
- gullible
- horrible
- indelible
- intelligible
- invincible
- legible
- negligible
- perceptible
- permissible
- plausible
- possible
- resistible
- responsible
- reversible
- sensible
- suggestible
- susceptible
- tangible
- terrible
- visible
Negatives of these words are naturally also spelt with -ible: e.g. inaudible, irresponsible.