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I've seen a thread that generally asks about Creating words with “-able” suffix But I don't think it answers my point, though they are admittedly dangerously close topics.

When do you drop the 'e' when forming words suffixed with -able. My Spell checker likes Unforgivable but dislikes Forgivable. Dropping the 'e' in the first case, and adding it in the second makes my spell checker happy. How do you determine when one is ok? Note that this is different from the linked question, where neither with or without the 'e' is accepted.

(Having checked the OED it seems there is one accepted spelling of Forgivable but two of Unforgiv(e)able)

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Did you read this answer? –  Jim Jan 18 '12 at 17:02
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@Jim I did, but only really focuses on hyphenation. What do you want me to get from that answer that I've missed? –  Pureferret Jan 18 '12 at 17:13
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@FumbleFingers: While, humph, if "forgivable" is a "pretty rare word" to you compared to "unforgivable", I guess that just says something about the kind of person you are. :-) –  Jay Jan 18 '12 at 17:38
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Did you read this answer? –  RegDwigнt Jan 18 '12 at 18:33
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@Pureferret No, it doesn't, but that difference exists in your spellchecker, which isn't necessarily the correct way to write it. It's just what that particular spell-checker thinks is right (which in this case is inconsistent). –  Jim Jan 18 '12 at 19:09
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3 Answers 3

up vote 12 down vote accepted

The only situation that comes to mind where an -e- is absolutely required before -able is when it modifies the pronunciation of a consonant, typically g or c:

Manageable (g as in giant) versus
*managable (g as in gut)

Traceable (c as in once) versus
*tracable (c as in cut)

Of course, that problem would exist in reverse for -ible words, but in practice it doesn’t arise as these are less common than their -able cousins.

The -e- also serves to make a vowel long where otherwise it could be interpreted as short. Scrapeable definitely begins with scrape, scrappable definitely begins with scrap, but scrapable could go either way; and if the common misspellings of short-vowelled words ending in -able are any evidence, it is likely to be read as scrappable.

In addition, when adding -able to words that end with a syllabic consonant, the -e- tends to be retained, to stress that the consonant still comprises its own syllable. tchrist offers:

Throttleable, (un)settleable, (un)whistleable, (un)riddleable

To my mind, whistlable is three syllables—[wɪs.lə.bɫ]—whereas whistleable is four: [wɪs.l.ə.bɫ]. That says nothing about which one I’d choose, because my pronunciation varies freely between them. Although, I do think that a two-syllable pronunciation of “settlers” (thus a three-syllable “settlable”) sounds rather Southern or Southwestern.

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+ scrapeable/scrappable is a good example. It's a shame we don't use a verb "to cape" (form into a cape, perhaps). There was discussion over whether the Deepwater Horizon leak could be capped ("cappable"), so given we've already got the totally unrelated word capable, that would really set the cat among the pigeons! –  FumbleFingers Jan 18 '12 at 17:29
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Ah, interesting point. Let me clarify for you that there is a general rule that when "g" or "c" is followed by "e", "i" or "y" it has the soft sound (g->j, c->s), but when followed by any other letter it has the hard sound (c like k, g like ... g). –  Jay Jan 18 '12 at 17:30
    
dictionary.com gives "scrapable" as the correct spelling for a word meaning "able to be scraped". I couldn't find any listing for "scrappable", though one would think that this would be a perfectly good word meaning "suitable for turning into scrap", as in, "Once we remove the motor the wire should be scrappable." –  Jay Jan 18 '12 at 17:36
    
@Jay: The fact that any particular inflected form isn't explicitly given by any particular (or indeed every) dictionary doesn't necessarily mean it's not a "valid word". In the case of scrappable here are hundreds of written instances. And it'll be far more common in things written later than the stuff indexed in Google Books. –  FumbleFingers Jan 18 '12 at 18:26
    
@FumbleFingers: I meant that I couldn't find "scrappable" in any of the several dictionaries I checked, not just that one I mentioned where I found "scrapable". Quite true that the failure of a word to appear in any particular dictionary does not prove that it "isn't a real word", but it would be an indication that it is unusual or specialized. What I was trying to say was that that surprised me. It seemed like it should be a fairly common word. –  Jay Jan 18 '12 at 20:11
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When I was in elementary school I was taught that the rule was: If a word ends with a silent "e" that serves to make the previous vowel long, and you add a suffix that begins with a vowel, drop the "e". If the suffix begins with a consonant, do not drop the "e".

Thus: forgive + able = forgivable

But: forgive + ness = forgiveness

Here's an Internet source that states this rule like this, "Another thing to keep in mind is that when a suffix is added that begins with a vowel and the main words ends with a silent "e", that silent "e" should be dropped like it is in the words pricing and surprising. However, if the suffix used begins with a consonant, the silent "e" should be kept such as in the words likeness and advancement." [http://www.thefreelibrary.com/English+Spelling+Rules+Adding+Prefixes+and+Suffixes-a01073900597]

thefreedictionary.com gives the spellings as "forgivable" and "unforgivable" -- no "e" in either word.

But frankly I often see spellings that do not follow this rule. Whether this is because people are not following a consistent rule or the rule as I was taught was a simplification and there are other cases, I can't say.

By the way, another general rule I learned is that when adding a suffix that begins with a vowel, if the base word ends with a short vowel followed by a single consonant, double the consonsant. If the vowel is long or there is more than one consonant, don't double the consonant.

For example, big + er = bigger. But cool + er = cooler (the vowel sound is long) and bank + er = banker (two consonants). (Ooh, I just noticed that I am using the suffix -er with two different meanings: "bigger" means "more big", but "banker" does not mean "more bank". In "cooler" it can have either meaning: more cool, as in "Today is coooler than yesterday", or a thing that cools, as in, "Put the soft drinks in the cooler.")

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Yes, there are other cases. The OED attests quite a few that fit no simple model. See my other comment. –  tchrist Jan 18 '12 at 22:33
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Definitely, there is no single rule or even a set of rules that can be applied consistently and algorithmically in all cases.

At least the set (un)forgiv(e)able seems to have started the process of shedding the e c1880. I do not yet know for sure what happened around 1880, though.

nGram forgivable | forgiveable | unforgivable | unforgiveable 1800-2000
enter image description here

What is surprising to note, however, is that the e does still survive, apparently fighting back.

nGram forgiveable | unforgiveable 1960-2000 enter image description here

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