A suffix is a letter or group of letters added at the end of a word in order to modify the meaning or part of speech of that word. The word "suffix" is a noun and is derived from the Latin past participle "suffigere," which means to attach on top of.
Silent E Rule
When a word ends with a silent "e," in most cases the "e" should be dropped if the suffix begins with a vowel, but the "e" should be kept if the suffix begins with a consonant. Exceptions include adding the suffixes "ous" and "able" to words that end in "ce" or "ge," including outrageous, noticeable and traceable.
Final Consonant Rule 1
This rule pertains to one-syllable words that end with a consonant vowel consonant combination. If you are adding a suffix that begins with a vowel, then you would double the final consonant. But if you are adding a suffix that begins with a consonant, do not double the final consonant. For example, if "allot" is the root word, you would double the final consonant to spell "allotted" and not double the final consonant to spell "allotment."
Final Consonant Rule 2
Words with more than one syllable that end with the consonant vowel consonant combination follow the same rule as Final Consonant Rule 1 as stated above, but only when the word is accented on the final syllable. Words with more than one syllable without the accent on the final syllable, such as refer and confer, do not follow the rule of doubling the final consonant before a suffix beginning with a vowel. Some exceptions include words that, under the rule, would not normally double the final consonant but do anyway. These exceptions include "equipped," "excellence" and "cancellation."
Final Y Rule
How to add a suffix to a word that ends in "y" depends on what precedes the "y." If the "y" is preceded by a consonant, then the "y" must be changed to an "i" when adding a suffix, unless it is the suffix "ing," in which case the "y" should remain unchanged. If the "y" is preceded by a vowel, then the "y" does not need to be changed to an "i" before adding the suffix. For example, "steady" would become "steadier" and "steadying," while "display" would become "displayed" and "displaying."