The Farlex Grammar Book > English Spelling and Pronunciation > Spelling Conventions > Affixes > Suffixes > Commonly Confused Suffixes > Commonly Confused Suffixes: -able vs. -ible
Commonly Confused Suffixes: -able vs. -ible
Words ending in “-able” or “-ible”
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.
Using “-able” with existing words
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:
- speak→speakable (especially used in unspeakable)
- think→thinkable (especially used in unthinkable)
Spelling changes with words that take “-able”
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.
Omitting silent E
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:
Keeping silent E before “-able”
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:
With other vowel suffixes
C + Silent E
danced, dancer, dancing
traced, tracer, tracing
G + Silent E
changed, changer, changing
managed, manager, managing
(*In British English, the silent E is usually kept in the word ageing, whereas it is usually omitted in American English.)
While most common when coming after C/G + E, this convention of keeping E before “-able” does occur after other consonants as well. However, this is quite rare and, in many cases, is simply an alternative spelling (especially in American English, in which E is much more likely to be omitted).
Here are some examples in which you might see “-able” following a silent E:
- file→fileable (but not filable)
- fine→fineable (more commonly, finable)
- like→likeable (more commonly, likable)
- live→liveable (more commonly, livable)
- love→loveable (more commonly, lovable)
- name→nameable (less commonly, namable)
- shape→shapeable (more commonly, shapable)
- size→sizeable (more commonly, sizable)
- trade→tradeable (more commonly, tradable)
Doubling consonants before “-able”
When the last syllable of a verb contains a single short vowel followed by a single consonant, we usually have to double the consonant before “-able.”
Note that, in multi-syllable words, this is only the case if the final syllable is stressed in the base word. Otherwise, the final consonant is not doubled, as in answerrable, cancelable, limitable, etc.
Replacing “-ate” with “-able”
We already saw that many verbs ending in “-ate” will take the suffix “-able” by omitting silent E. However, there are also quite a few words in which “-ate” is replaced altogether. Unfortunately, there is no spelling pattern we can use to indicate which “-ate” words will be changed this way; we just have to memorize them. Here are some of the most common:
- alienate→alienable (especially in the word inalienable)
Changing Y to I before “-able”
When a suffix beginning with a vowel is attached to a word ending in a consonant + Y, we almost always change Y to the letter I. Because of this, verbs that end in “-y” always take the “-able” suffix, since we never have a word spelled “-iible.” Let’s look at some of the most common examples:
There are also two nouns ending in “-y” that can take “-able,” but Y no longer changes to I—it is simply omitted:
Using “-able” and “-ible” with incomplete Latin roots
Because “-able” is so commonly used with existing base words, the most common tip to remembering the “-ible” variation is that it is usually used with Latin roots that cannot stand alone as words.
However, this is not a very reliable convention, because “-able” also attaches to many incomplete Latin roots (though “-ible” does so more commonly). There is only one rule we can use to know which ending is correct: if a root ends in a “soft” C (/s/) or G (/ʒ/), it will always be followed by “-ible,” while a “hard” C (/k/) is always followed by “-able.” (No Latin roots will end in a “hard” G, /g/.) Unfortunately, we just have to memorize the rest of these types of words:
Latin root + “-able”
Latin root + “-ible”
corrigible (most commonly used in incorrigible)
(*Note that the root fall- here is not the same as the verb fall.)
Using “-ible” with existing words
Though much less common than “-able,” the “-ible” variant can also attach to existing base words with no change to its spelling. As with the Latin roots, there are generally no indications in the base word’s spelling to indicate when “-ible” is correct, except for one: base words ending in “-uct” will (almost) always take “-ible” rather than “-able.”
Let’s look at some examples:
- controvert→controvertible (especially in the word incontrovertible)
(Because “-able” is a productive suffix, meaning it is still being used to create new words, there may be instances in the future in which this rule is no longer true. For example, the term instructable has been gaining in popular usage in the last 30 years, but it is not found in the dictionary; instructible, meanwhile, is in the dictionary but has nearly become obsolete, which is why it isn’t included above.)
“-ible” with silent E
Like “-able,” the “-ible” ending can also replace silent E at the end of existing base words, as in:
However, as you can see by the size of the list, it is much less common for a silent E word to take “-ible” rather than “-able.” If a word ends in a silent E, it will most likely take the “-able” suffix (and base words ending in “-ate” can only take “-able”).
Other spelling changes with “-ible”
Sometimes an “-ible” word is related to an existing base word, but the spelling must change slightly to accommodate it. This also occurs with certain words when they attach to “-able” (e.g., when the suffix replaces “-ate” or “-y” becomes “-i-”), but “-ible” can result in much more drastic changes to the spelling of the base word.
The most consistent of these changes is for verbs ending in “-mit”: with the exception of limit (which becomes limitable), all of these verbs take the “-ible” ending, with “-mit” changing to “-missible.” Another common change occurs with verbs ending in “-nd,” which changes to “-nsible” (however, other verbs ending in “-nd” can take “-able” instead, so we can’t use this verb ending as a rule to determine the appropriate suffix). In addition to these, two other specific words have their endings change when attached to “-ible.” Let’s look at all the words that go through spelling changes with the “-ible” suffix:
“-mit” + “-ible”
“-nd” + “-ible”
Other endings + “-ible”
remit→remissible (slightly different meaning from remittable)
defend→defensible (slightly different meaning from defendable)
perceive→perceptible (slightly different meaning from perceivable)
Words that can take either “-able” or “-ible”
In addition to the trends we’ve seen above, there are words ending in “-able” that can alternatively be spelled “-ible,” and vice versa. In most cases, these are simply less common variants; other times, the meaning of the word is very similar but subtly different, depending on the ending used.
The table below shows all words that have acceptable variant spellings. For each pair, the most common spelling is in bold; if one is much more common than the alternative, it will be bold and underlined. Finally, if the two spellings have slightly different meanings, they’ll be marked with an asterisk (*) and elaborated upon further on.
Ending in “-able”
Ending in “-ible”
*These pairs of words have slightly different meanings, which we’ll look at next.
defendable vs. defensible
Defensible is the much more common adjective derived from the verb defend, but defendable is an acceptable variant. While they can be used nearly synonymously, there is actually a slight difference in their overall meanings. Defensible is generally used to describe something that is capable of being defended through logical (i.e., non-physical) means, such as an idea or a decision. While it can also relate to physical defense (such as in combat), the former meaning is much more common.
Defendable, on the other hand, is almost solely used to describe physical defense. Even in this use, though, it is a much less common variant of defensible.
eatable vs. edible
The words eatable and edible are nearly identical in meaning, but there is a subtle distinction in the way each is applied.
Edible most commonly used to describe something that is fit to be eaten. For example, a piece of fruit is edible, but imitation plastic fruit is inedible.
The variant eatable, on the other hand, is typically used to refer only to the desirability of being eaten, rather than it being physically fit to be eaten. Something edible (capable of being eaten without causing harm) might be so repellent due to flavor, preparation, or texture as to be completely uneatable. However, even with this distinct meaning, edible is vastly more common than eatable. Additionally, edible can be used figuratively to achieve the same meaning, so unless you have a specific reason not to, you should always use edible.
perceivable vs. perceptible
Like defendable and defensible, perceivable and perceptible are separated by a cognitive, non-physical aspect in meaning. Perceptible, the more common of the two, means “capable of being perceived,” whether by physical senses (such as touch, sight, or hearing) or cognitive senses (such as being able to notice when a person’s behavior begins to change). Perceivable, on the other hand, is generally only used in reference to physical perceptions, not cognitive ones. As with defensible and edible, perceptible is much more common and has a broader meaning than its variant, making it the preferred spelling overall.
remittable vs. remissible
These two words are both derived from the verb remit, but are applied to different meanings the verb can have.
Remissible is the more traditional of the two adjectives, and it means “able to be pardoned or forgiven.” Remittable takes the more modern meanings of remit, “capable of being transferred (such as a payment)” or “able to slacken, abate, or relax.”
Remissible used to be the more common of the two, but in recent years it has been overtaken by remittable, likely due to the ubiquity of the productive “-able” suffix and the broader meaning of remit that it implies.
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