Republican and Democrat Next post: Learning from the debate transcripts of Mitt Romney and Barack Obama

glissandos Previous Post: Glissandos and glissandon’ts

Should you add 'ible' or 'able' to end of 'fashion'?

Do you know your -ibles from your -ables?

If you’re a regular reader of this blog, you may recall that we’ve featured postings on homophones over the past few months, but all of them have been complete words, such as pedal and peddle. Of course, suffixes (word endings) and prefixes (word beginnings) can also sound the same in English, causing no end of puzzlement when it comes to spelling. For instance, people often have no idea whether a word such as independent ends with –ent or –ant (it’s -ent, but the Oxford English Corpus (OEC) has almost 800 examples of the erroneous  independant). Similarly, for- and fore- can cause spelling problems: there are 49 instances of forcast (instead of forecast) on the OEC.

But don’t despair! Help is at hand: I’m going to look at some homophonous prefixes and suffixes over the next few months and offer some spelling tips to help you make the right choice.

Let’s start with a pair of endings that many people find confusing: -able and -ible. These suffixes are usually used to form English adjectives. They sound very similar when you say them and they share a main meaning, which is ‘able to be’:

readable able to be read; easy to read
eatable able to be eaten; fit to be consumed as food
audible able to be heard
collapsible able to be folded into a small space

Why are there two different endings that mean the same? It’s because of the route by which these endings found their way into English. The suffix -able comes from French -able or Latin -abilis, while the ending –ible comes from French –ible or Latin –ibilis.

-able words

This ending was originally found in words that came into English direct from French or Latin terms, for example measurable, from Old French mesurable, from late Latin mensurabilis. Later, –able was used to form adjectives directly from English verbs that ended in -ate, such as educable from educate.

More recently, -able has been used to create adjectives from verbs of all types (e.g. bearable, adaptable): this is because of the influence of the unrelated word able. There are also a few -able words, such as peaceable, fashionable, and marriageable, that are formed or partly formed from nouns. Because -able is still used to create English words today (such as bloggable), it’s termed a productive suffix.

Tip one

This tip is based on sheer weight of numbers:  as a very general rule of thumb, if you choose -able, you’re more likely to be correct. This is because there are hundreds more words spelled with the suffix –able: our online dictionary of current English has around 180 adjectives ending in –ible, compared with over 1,000 that end in -able. If you’re not sure, however, it’s always best to look the word up in a dictionary.

Tip two

If the stem (the main part of the word that comes before -able or -ible) is a complete word in itself, then the ending is nearly always -able. A simple test is to take away the suffix – does the word still exist as an English word? For example:

-able  or –ible adjective Word remaining when ending is removed?
readable ✓ read
acceptable ✓ accept
treatable ✓ treat
changeable ✓ change
dependable ✓ depend
audible ✗ aud
edible ✗ ed
horrible ✗ horr
tangible ✗ tang
feasible ✗ feas

This rule is also applicable when the stem:

  • ends in an e that’s dropped before -able is added (e.g. advise → advisable)
  • ends in a consonant that’s doubled when –able is added (e.g. forget → forgettable)
  • has two syllables or more and ends in -ate  [to form the adjective, drop -ate and add-able (e.g. calculate → calculable; demonstrate → demonstrable)].

Inevitably, there are a few exceptions to these rules and you just need to learn the spellings: the main ones are capable, durable, and equable.

Tip three

If the main part of the word ends with a ‘hard’ c (pronounced like the c in cut) or a ‘hard’ g (pronounced like the g in get), the ending is always –able:

Hard c Hard g
amicable navigable
despicable indefatigable
practicable delegable

-ible words

Most –ible words derive directly from Latin ones (audible comes from late Latin audibilis) or they derive both from French and Latin (possible comes from either Old French possible or from Latin possibilis).  The Oxford English Dictionary gives this useful advice:

. . .in English there is a prevalent feeling for retaining -ible wherever there was or might be a Latin -ibilis; while -able is used for words of distinctly French or English origin, as conceivable, movable, speakable.

Tip one

The good news is that the suffix -ible isn’t used today to form new terms, so you only need to know a limited set of -ible words (yay!). Here are some of the most common ones:

accessible eligible invincible responsible
audible expressible legible reversible
collapsible feasible negligible risible
contemptible flexible ostensible suggestible
convertible gullible perceptible susceptible
digestible horrible permissible tangible
divisible incredible plausible terrible

Of course, you can add prefixes to most of these words to form other adjectives, such as im– plus possible = impossible. In fact, the only new words ending in -ible are those which are coined by adding a prefix to a word that already exists as an -ible adjective, such as biocompatible, which the Oxford English Dictionary tells us was formed from compatible and the prefix bio- in about 1970.

Tip two

This is related to Tip two for -able, above. As you can see from that table, when a word ends in -ible, the main part is much less likely to be a recognizable word in English (for example ‘terr’ is not a word). Again, there are a few exceptions to this rule which you just need to learn: the main ones are accessible, suggestible, collapsible, flexible, and digestible.

Contractible collectibles

There’s a very small set of words which you can spell with either -able or -ible, such as extendable and extendible: both mean ‘able to be extended’ and both endings are acceptable. Any good dictionary will provide both spellings if they are equally correct.

Sometimes, the different spelling relates to a different meaning: it’s therefore especially important to pick the right ending. For instance, contractable means that a disease is able to be contracted (or caught):

The virus is highly contractable.

while contractible means that something is capable of contracting (becoming smaller):

A container having a contractible body for storing a liquid is provided.

As you can see from these examples, a container would never be contractable!

Finally, collectable is an interesting case. It can be an adjective and a noun and both can be spelled collectible. As an adjective, collectable has two meanings. The spelling collectable is usually used to mean ‘able to be collected’:

The board reckons another $2.4 million is collectable, to be dished out to shareholders over the next three years.

whereas the spelling collectible is usually means ‘worth collecting; interesting to collectors’:

He was also an accomplished driver, and an expert on antique and collectible toys.

The noun only has one meaning: ‘an object that’s valued by collectors’. The spelling collectible is far more common for the noun: the OEC has over 1,200 instances, compared to around 330 for collectable. Although you wouldn’t be wrong if you chose to spell the noun with the ending -able, you’d be out of step with the majority of people. Who knows, we may eventually see collectable as a noun become even rarer and perhaps fall out of use completely.



The opinions and other information contained in OxfordWords blog posts and comments do not necessarily reflect the opinions or positions of Oxford University Press.