What to use? -able or -ible?

Comparison between "-able" and "-ible"

-able vs -ible

What are "-able" and "-ible" ? 

Both are called "suffixes". Suffixes are a letter or group of letters added to the ending of words to change their meaning or function. These useful, shapeshifting tools can be as small as -s, and -ed, or can be larger additions such as -ation, and -ious.

Rule of thumb

- If you remove -able from a word, you are left with a complete word (renewable, renew).

- If you remove -ible from a word, you are not left with a complete word (sensible, sens). But note that accessible, contemptible, digestible, flexible and suggestible are among the exceptions to this rule.

The most common -ible endings

	Adjectives ending in (-able)	Adjectives ending in (-ible)
Examples	Navigable, affordable	Comprehensible, permissible
When to use	companion word ends in -ation: abomination -> abominable irritation -> irritable	When companion word ends in -ion comprehension -> comprehensible digestion -> digestible
	after hard c and hard g  practicable, amicable (c sounds like k) navigable (hard g)	after soft c and soft g forcible (c sounds like s) legible (g sounds like j)
	If the base word (the main word without -able) can be a complete part on itself (even when e is dropped, or a consonant doubled when adding -able bear - bearable read - readable accept – acceptable advise – advisable inflate – inflatable forget – forgettable regret – regrettable	If the base word (the main word without -ible) can’t make a meaning on its own. Audible – aud Permissible – permiss Illegible – illeg Incredible – incred Exceptions of the rule: accessible, collapsible, contemptible, digestible, flexible, suggestible, illegible

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Why Suffix Choice Matters in English Spelling

Choosing between -able and -ible is one of the most common spelling challenges in English. Both suffixes create adjectives that mean "capable of being" or "worthy of," but they follow different historical patterns. English borrowed many -ible words from Latin, which is why they often appear in more formal or academic vocabulary. The -able suffix, on the other hand, attaches freely to existing English verbs, making it far more productive in modern word formation.

Understanding the origin of a word often gives you the strongest clue. Words ending in -ible usually come from Latin roots that were already complete words (like audire meaning "to hear," giving us "audible"). Words ending in -able typically attach to verbs that exist independently in English or in Latin verb forms that were commonly combined with this suffix.

Additional Spelling Patterns to Watch For

Another helpful pattern: when a word ends in -ation in its noun form, the adjective form usually takes -able. For instance, "abomination" becomes "abominable," and "irritation" leads to "irritable." Conversely, when the noun form ends in -ion (without the -at prefix), the adjective form often takes -ible: "comprehension" becomes "comprehensible," "permission" becomes "permissible," and "digestion" becomes "digestible."

There are also words where the base word before the suffix is recognizable but modified. For example, "bear" becomes "bearable" (the silent e is dropped), while "incredible" has no standalone base word "incred." When in doubt, check whether the root word stands alone. If it does, -able is the safer bet. Hard consonant sounds (hard c as in "k" and hard g) also tend to favor -able, while soft c (sounding like "s") and soft g (sounding like "j") tend to favor -ible.

Key Takeaways

• Remove the suffix: if the remaining word is a complete word, use -able.
• If the remaining fragment is not a word, use -ible.
• Nouns ending in -ation typically take -able as the adjective suffix.
• Nouns ending in -ion (without -at) typically take -ible.
• Hard consonant sounds (hard c and hard g) favor -able; soft sounds favor -ible.
• Exceptions exist, such as "accessible," "flexible," and "suggestible," which require memorization.

Frequently Asked Questions

How do I remember which suffix to use?

The most reliable trick is the "remove the suffix" test. If you strip -able and the remaining part is a real English word, use -able. If stripping -ible leaves a fragment that is not a word, use -ible. For example, "bearable" leaves "bear" (a word), so it is -able. "Sensible" leaves "sens" (not a word), so it is -ible.

Are there words where both spellings appear?

Rarely. In modern standard English, each word has one accepted spelling. However, some words have historical variant spellings that are no longer common. Always consult a reliable dictionary when unsure.

Does American English differ from British English here?

The -able vs -ible distinction is largely the same in both American and British English. The same rules and exceptions apply regardless of which variety you are writing.

Why do some words like "flexible" and "accessible" break the rule?

These are exceptions inherited from different Latin verb conjugations. "Flexible" comes from the Latin flexibilis, and "accessible" from accessibilis. Because these Latin forms already ended in -ibilis, English retained the -ible spelling even though "flex" and "access" look like standalone words.

Can I use a dictionary to check?

Yes, and you should. A good dictionary is the final authority on spelling. When you encounter a new word, look it up and note whether it ends in -able or -ible. Over time, the patterns will become more familiar.