The suffixes “-able” and “-ible” are both used to form adjectives meaning “possible, capable of, suitable for, or causing.” Of the two, “-able” is much more common: it is what’s known as a “living” or “productive” suffix, meaning that it is still being used to create new words. The variant “-ible,” on the other hand, is only used in older words that have survived into modern English.
Because they are spelled so similarly and have the same pronunciation ( /əbəl/ ), it can sometimes be hard to remember which is the correct one to use. Unfortunately, there are not very many conventions we can follow to know which suffix to use (and those that do exist are not always reliable). Instead, this section will focus on the different ways “-able” and “-ible” each attach to words, along with many examples for each.
The suffix “-able” most commonly attaches to words (most often verbs) that could otherwise be complete without the suffix; in many cases, this occurs with no change to their spelling. Because “-able” is a productive suffix, there is a huge number of words it can be attached to. Let’s just look at some common ones:
While many base words can take the “-able” suffix without changing their spelling, there are also many instances in which the spelling must be altered slightly in order for the suffix to be attached. The most common of these occur with words ending in silent E, but there are other instances in which a word’s spelling will change in various ways.
The most common spelling change made to a word when “-able” is attached is for silent E to be omitted from the end of the word and replaced with the suffix (though this is not always the case). For example:
Note that there are many instances in which we do not omit a silent E when adding the vowel suffix “-able.” This is especially true when it comes after C or G to make it clear that the consonants retain their “soft” pronunciations (/s/ and /ʒ/ , respectively). For example: