Is there a pattern for -able verbs turning into -ible?

Question

So there is the "-able" suffix for verbs, but some verbs take "-ible" instead. Is there a rule for which verbs would take which form? Perhaps depending on the pronounciation of the verb?

Answer 1

Not really.

In Latin there are suffixs -abilis and -ibilis, and these were regular, depending on the vowel in the inflection of the Latin verb. The first conjugation "poto" (second person potas) becomes "potabilis", but the third conjugation "edo" (second person edis) become "edibilis". These resulted in -able and -ible forms in French. Most of the English words ending in -ible are derived from French. In fact the Latin suffix is really -bilis, with the -a- or -i- actually being part of the verb.

In English we have potable and edible.

So you can't really tell unless you happen to know the conjugation of the Latin verb that the word comes from, and even this isn't a guarantee, as some were changed between -ible to -able at some point in history.

When used productively (for making new words) -able is usually used. For example "drinkable". If the base word isn't from Latin, you can be confident that "-able" is the correct form.

Note that -able as a suffix is not etymologically related directly to the word "able", although the similarity in meaning has surely influenced the use of the suffixes.

Answer 2

There isn't a hard and fast rule but the general pattern most sources (such as Lexico and Grammarist) give is that the removal of -able results in a recognisable and complete English word (e.g. 'emailable' -> email + able; email is a complete and recognisable word) whereas the removal of -ible often results in an unrecognisable word (e.g. audible -> aud + ible; aud isn't an English word). Moreover, -able is attachable to an enormous number of verbs as it's a living suffix. According to Grammarist "affix it [-able] to virtually any verb without using a hyphen, while -ible is not used to make new words. It lives on mainly in old words passed down through the centuries."

Another thing to note is that verbs ending in a hard G (as in 'gate') and a hard C (as in 'cat') almost always take -able. As always, there are loads and loads of exceptions.

Answer 3

Able vs Ible Learn many things in English. There are many complex principles regarding the proper use of prefixes and suffixes.

Related to the latter, there are often two suffixes that are confused with each other. These are suffixes for "able" and "ible".

For those who are used to writing in English, it is not difficult to distinguish when to use another language. Once you get used to it, you don't need to pay attention to the rules behind usage.

But for starters, there are some rules to follow when using the suffixes "able" and "ible" with certain roots.

Rule 1 – It is safe to add the suffix "able" if the root itself appears to be a complete word.

Rule 2 – If the root is not a fully spelled word, use the suffix “ible”.

These rules are best shown in the following examples. In the word "acceptable", the suffix "able" is used because the word "accept" as a root is a fully spelled word. So it would be inappropriate if people use "acceptable" like "acceptable".

For the second rule, the word "compatible" uses the suffix "ible" because the root word "compat" is not a complete word. That's why using the suffix "able" to "compat" makes the final word "compatable" also inappropriate.

Rule 3 – Still, if the root ends with the letter "e", remove that letter before adding "able", just like the word "advisable" becomes "advisable".

Continue Reading...