- If the base word is a complete and recognizable word, usually use -able.

- If 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.

- If you must double the final consonant of the base word or change the final -y to i, add -able.

- The suffix -ible is less common and the base word is not a complete and recognizable word.
NB: There are some exceptions.