1. Words of one syllable (and words of more than one syllable if accented on the last syllable), ending in a single consonant preceded by a single vowel, double the first consonant before a suffix beginning with a vowel.
| thin | thinner | forgot | forgotten |
| slap | slapping | trot | trotting |
| acquit | acquitting | begin | beginner |
2. When the accent is thrown back upon another syllable, after the derivative is formed, the final consonant is not doubled.
| refer | reference |
| prefer | preference |
3. When preceded by two vowels, the final consonant is not doubled.
| toil | toiling |
| keep | keeper |
III. For final y.
1. Words ending in y, preceded by a consonant, retain y before a suffix beginning with i; on taking a suffix beginning with any other letter, y is in most cases changed to i.
| cry | crying | lazy | laziness |
| fly | flying | duty | dutiable |
| try | trying | happy | happiness |
2. Words ending in y, preceded by a vowel, retain y before a suffix.