Suffixes cause many of our common spelling mistakes. One challenge is simply to know which is correct: for example, legible or legable? In fact, −ible and −able serve the same function, and sound the same. As a matter of history, -ible entered English from Latin, while −able entered English from French, but there’s no easy rule for knowing when to use which suffix. Each word with each suffix just requires practice.
Adding an English prefix to a word is often straightforward. For example, we can add super− to reliable and get superreliable. The same is not always true of suffixes.
When we add suffixes to existing words, the new combination can affect spelling in various ways. The result may be a doubled consonant, or a combination of vowels. As a consequence, we may be required to remove a vowel or consonant from the original word or to replace one letter with another. If you know the general guidelines for adding suffixes to existing words, you will be more confident in your own spelling. The next section will help you review some of the key rules related to suffixes.