How Verbs Become Adjectives

By Mark Nichol

What determines whether a verb-to-adjective transformation ends with the suffix -able (as in assessable) or with -ible (as in accessible)? Why do some root words accept both options? What happens if the word ends with an e? Answers to these and other questions about -able and -ible follow.

The suffixes -able and -ible both express capability, fitness, or worth (or mean “tending, given, or liable to”), but there’s one key practical difference: The former flourishes, and the latter has fossilized. New words can be formed by attaching -able to an adjective (I’ll get back to that in a moment) — or a noun (more about that later, too) — but -ible, though widespread in existing words, is discouraged for new coinages.

Some words use one form unequivocally. (For example, immovable and invincible are never rendered immovible and invincable). Others are spelled either way, although one form predominates (as in the case of discernible and its less frequent variant discernable). In some cases, the variants reflect a distinction of meaning: For example, collectable means “able to be collected,” but the more common collectible has the connotation of desirability and is used as a noun to denote something worth collecting.

Intransitive verbs can also be transformed into adjectives by appending -able. Strictly speaking, reliable, for example, means “able to be relied on,” not just “able to be relied,” but the needs of the language have silenced opposition to such usage. Adjectives are also formed from attaching -able to nouns, such as objectionable from objection, though the nonword objectable is the logical formation based on the verb-plus-able formula.

Two other peculiarities exist regarding the suffix: When it is appended to a verb ending in -ate, such as calculate, the original suffix is omitted, resulting, for example, in calculable (which is overshadowed in frequency of usage by its antonym, incalculable). And when a word ends in e, such as in the case of move, the e is omitted when -able is attached, hence movable. (You’ll see moveable and the like in older publications, but this form is rare in contemporary usage.) Exceptions occur when a soft c or a soft g precedes the e, as in serviceable and changeable.

When coining new terms, keep these rules in mind — though consider, as well, that even some existing words, such as embraceable, are ungainly, and newly minted terms may be disagreeable to some readers.

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6 Responses to “How Verbs Become Adjectives”

  • Dale A. Wood

    Some verbs become adjectives by adding one or more prefixes ending in “ary”.
    E.G. “probate” + “tionary” = probationary
    E.G. “found” + “tionary” = foundationary:
    The attorney presented foundationary evidence so that she could ask the BIG QUESION of witness.

    I am sure that there are more, but I am having a hard time coming up with them offhand.

  • Dale A. Wood

    Do not pay too much attention to what spell-checkers say concerning whether something is a vaild word or not. Dictionaries and your memory from wide reading always override mere spell-checkers, all of which have many omissions.

    I often use a spell-checker in an e-mail program that omits these
    {gauge, superluminal, Rebecca, Los, Angeles, Las, San, venusian, jovian, saturnian } and many other useful and common words. It is especially bad in scientific vocabulary. Also, it is very strange that the company that made this program is located in California, yet we run into bad indicators of misspelled words for the names of hundreds of places in California, Mexico, New Mexico, and South America! “Bernardino” is omitted, too, but “Vegas” is there.

    Also, the spell-checker omits the fact that:
    Monterey is an important county and town in California, but
    Monterrey is a large and important city in northern Mexico. Only one of these words is completed. A present ship in the U.S. Navy is named the USS “Monterey” – after the Battle of Monterey in Monterey County, when the Californians were rebelling against their Mexican rulers.

    Did the compilers of that spell-checker think that “gauge” is really spelled “gage”? If you are unfamiliar with the word “gauge”, think of these: air gauge, fuel gauge, gas gauge, pressure gauge, rain gauge, water gauge, and wind gauge.
    I imagine that in England and Scotland they even have “petrol gauges”.

  • Dale A. Wood

    Don’t forget that some verbs become adjectives by the addition of “tion”, “sion”, or “cion”.
    E.G. The verb “suspend” becomes the adjective “suspension”:
    There is a magnificent suspension bridge over the mouth of San Francisco Bavy.
    E.G. “Elevate” becomes “elevation”: When describing the location of an object on the sky, the two numbers you need are the elevation angle and the azimuth angle w.r.t. due north.
    E.G. The verb “populate” becomes “population”: You really ought to read the book “The Population Bomb”.
    E.G. The verb “educate” becomes “education”: We need a much better education system in the United States, and my friends in England tell me that the problem is much worse there.

  • Dale A. Wood

    Past participle and present participles as adjectives:
    E.G.: The canned vegetable section of the grocery store was an odd place for Jack to find his missing cousins, Peter, Paul, and Mary. He had not seen them for 15 years.

    So many careless people use “can” instead of “canned”, even for the signs in supermarkets. The phrases are “canned peaches”, “canned carrots”, and “canned Spam”. There is even “canned music”. Have you heard any lately?

    Weird Al went to cooking school to learn all about the delights of canned pineapple, canned Spam, and diced sweet potatoes. He also learned how to make 10 kinds of baked lasagna.

  • Dale A. Wood

    Dear Author,
    Do not forget that most verbs in English become adjectives by adding “ed” or “ing”.
    In other words, we use the past participle or the present participle.
    E.G.: The stranded man swayed above the dangling net.
    Stranded – past participle; dangling – present participle.

  • thebluebird11

    Hmmm…you raised one point here that might explain my issue with injectable vs injectible. You mention the difference between collectable and collectible. I think that “injectable” is the run-of-the-mill word everyone sees; it’s an adjective meaning “able to be injected.” However, in the medical field we often need the noun (i.e. something that can be injected), so I would like to go with “injectible,” but according to my spellchecker, that word doesn’t exist. Do I have permission to use it?

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