Among educated people, there are only two things that people take pride in being ignorant about: math and spelling. I believe people are proud of their mathematical inability because they think it says they are creative and not rigid. The implication is that mathematics is rigid, but this belief is just further evidence that such people don’t get math. I was never like that, of course. But at one time, I provided myself a kind of apologia for being bad at spelling. According to it, spelling was an arbitrary system that was just a matter of memorizing thing and therefore had nothing to do with real thinking.

I had reasons for believing this. Most spelling rules seemed hopelessly riddled with exceptions. For example, “I before E, except after C.” Even when I learned the full rhyme I wasn’t helped, “I before E, except after C, or when sounding like A, as in neighbor or weigh.” But the problem was not actually that little rhyme. The problem was that no one ever taught me what it all meant. That little rhyme is actually shockingly helpful. I can’t offhand think of any examples when it isn’t true.

To -Able or to -Ible, That Is the Question!

As I’ve gotten older and become a far better speller, the things I struggle with has greatly decreased. And the one broad area of spelling that I still struggle with is when to use “able” and when to use “ible.” Luckily, I’ve found an excellent set of rules in The Grammar Bible by Michael Strumpf and Auriel Douglas. And if for no one’s benefit but my own, I figured I would go over it.

Let me start with a rule that is not in the book. It is not in the book because only the truly clueless would not know it. But given I went for decades of my life without knowing it, I think it bears noting. There is no “eble” ending. It isn’t a thing. I’m not saying that there are no words that end with “eble.” But the ending would not indicating being able to do whatever the root of the word indicated. If the word “breakeble” existed, it would not mean, “Able to be broken.”

Base Rule

The most basic rule is that if the root that you are modifying is a complete word, add “able.” So “avail” becomes “available” and not “availible.” If the root is not a complete word, add “ible.” So “incredible” is a word and “incredable” is not. And that’s all you have to remember. Oh, I’m kidding! It isn’t that simple. But it isn’t that much worse.

If the above rule indicates that you should add “ible” there is an exception. If the root ends with a hard G or C, then you should add “able.” Supposed you wanted to say “able to navigate” with one word. Since “navig” is not a word, we would think it ought to end with “ible.” But because “navig” ends with a hard G, we go with “able.” So “navigable” is the word and “navigible” is not. Notice, however, that it is a hard G. The word “illegible” has the “ible” ending, because “illeg” ends with a soft G.

Similarly, if the base rule indicates that you should add “able” there is an exception. If you can add “ion” to the root to create a proper word, you should add “ible.” So the word “suggest” can be turned into the word “suggestion.” Thus, the word to describe someone who is prone to suggestions is “suggestible” and not “suggestable.”

Silent E

Knowing these rules can take you quite a long way in spelling such words. But there is one aspect that it is still just crazy: root words that end with a silent E. Should you keep the E as in “changeable” or drop it as in “believable”? I wish there were some rule for this, but there really isn’t. Some people claim that more common words drop the E, which makes sense because the language does tend to simplify itself with use. There does seem to be something to this. All these words are pretty common: believable, pleasurable, desirable, lovable, conceivable. Then again: knowledgeable?

What’s more, all of these rules are of the thumb kind. There are still many exceptions. In fact, there are even exceptions to the silent E cases: responsible, reversible, plausible. Is there a rule about roots ending with S sounds? I don’t know. It does seem to be the case that you never keep the E when you add “ible.” But the point is that these rules will take you at least 80% of the way to correctly spelling such words. And the words that break the rules will stand out to you and you can make exceptions for them.