In every language, there are multiple spelling rules to follow when writing. An important spelling rule to know in English is what to do when adding a suffix to a word.
Before adding a suffix to a word, double the last letter of the word if all of the following conditions are present:
A: the root word ends with one consonant preceded by one vowel.
B: the suffix to be added begins with a vowel.
C: The syllable that ended the root word is stressed in the new word.
Examples requiring a doubled consonant
This following list are examples of words that respect all three conditions. Therefore, you must double the last letter of the root word before adding a suffix to it:
Begin + er = beginner
Occur + ence = occurrence
Repel + ent = repellent
Stop + ing = stopping
Submit + ed = submitted
Tranquil + ity = tranquillity
Examples requiring no doubling
This following list are examples of words that do not respect all three conditions. Therefore, you must not double the last letter of the root word before adding a suffix to it. The condition that is missing will be in parenthesis next to the word:
Defend + ed = defended (missing condition: A)
Endure + ance = endurance (missing condition: A)
Commit + ment = commitment (missing condition: B)
Develop + ing = developing (missing condition: C)
Confer + ence = conference (missing condition: C)
A few exceptions
In English, just as in French or any other language, often when there is a rule, there are exceptions to it which you must learn by heart in order to know how to spell a specific word. For example, inn Canadian English, travelling, signalled, and carolling are spelled with two l’s, even though they do not respect the three conditions of the spelling rule. Another word that does not conform to this grammar rule is enrol. While enrolled and enrolling both take two l’s, enrolment is spelled with only one l. The last word that goes against the rule is control: controlled, controlling and controller is spelled with two l’s.