Final silent -e
Generally, drop a final silent -e when adding a suffix that begins with a vowel.
combine, combination
desire, desiring
remove, removable
prude, prudish
Keep the final -e if the suffix begins with a consonant.
achieve, achievement
care, careful
entire, entirety
gentle, gentleness
EXCEPTIONS
argument, changeable, truly, judgment
Final -y
When adding -s or -d to words ending in -y, change -y to -ie when the -y is preceded by a consonant.
comedy, comedies
dry, dried
If -y is preceded by a vowel, simply add -s or -ed.
monkey, monkeys
play, played
With proper names ending in -y, however, do not change the -y to -ie even if it is preceded by a consonant: the Dougherty family, the Doughertys.
Final consonants
If a final consonant is preceded by a single vowel and the consonant ends a one-syllable word or a stressed syllable, double the consonant when adding a suffix beginning with a vowel.
bet, betting
occur, occurrence
commit, committed
If the final syllable is not stressed, then do not double the final consonant when adding a suffix.
travel, traveling
budget, budgeting
profit, profited