Words Ending in -able vs -ible: Spelling Rules

Why These Endings Cause Trouble

English has many word endings that sound alike, and -able and -ible are among the most frustrating. In speech, they are normally indistinguishable. In writing, one letter makes the difference between a standard spelling and a mistake: accessible, not accessable; dependable, not dependible. That is why even careful writers sometimes pause before typing them.

Fortunately, the choice is not pure guesswork. Most words follow recognizable patterns, although a smaller group has to be learned by memory. Once you know when -able is the safer default and when -ible is expected, these spellings become much easier to handle. This guide explains the rules, gives broad word lists, and offers practical memory tips. For a wider look at spelling patterns, see our guide to English spelling rules.

The Meaning Shared by -able and -ible

The suffixes -able and -ible both usually mean "capable of being" or "worthy of being." They are used to make adjectives from verbs and nouns:

• Wash (verb) + -able = washable, meaning capable of being washed
• Reason (noun) + -able = reasonable, meaning having or showing reason
• Access (noun/verb) + -ible = accessible, meaning capable of being accessed
• Flex (verb) + -ible = flexible, meaning capable of bending or being flexed

The two endings trace back to different Latin forms. The ending -able comes from Latin -abilis, often connected with first conjugation verbs, while -ible comes from -ibilis, associated with second and third conjugation verbs. That history helps explain why some modern spellings look irregular at first. Learning more about word roots can make these patterns easier to see.

The Main Pattern to Remember

The most useful shortcut is this: -able is much more common, and it is the normal choice for newly formed words. When a modern English word is turned into an adjective and no special rule points elsewhere, -able is usually right. English has roughly 900 words ending in -able, compared with about 200 ending in -ible. Newer formations also use -able: clickable, downloadable, microwaveable, recyclable, scalable.

Situations That Call for -able

Guideline 1: Use -able when the base is a complete English word

When you remove -able and what remains is a recognizable English word, -able is usually the correct ending. Examples include wash → washable, work → workable, suit → suitable, reason → reasonable, notice → noticeable, knowledge → knowledgeable, fashion → fashionable, depend → dependable, and comfort → comfortable.

Guideline 2: Drop a final -e before adding -able in most cases

Many words ending in silent -e lose that -e before -able is added: use → usable, love → lovable or loveable, move → movable or moveable, excite → excitable, debate → debatable, value → valuable, desire → desirable, advise → advisable.

There is an important sound-based exception. If the base ends in -ce or -ge, the -e is usually kept so the c or g stays soft: service → serviceable, replace → replaceable, knowledge → knowledgeable, trace → traceable, manage → manageable, change → changeable, notice → noticeable.

Guideline 3: Change final -y to -i before -able

Words ending in -y commonly change that y to i before the suffix is added: identify → identifiable, justify → justifiable, envy → enviable, deny → deniable, rely → reliable.

Guideline 4: With many -ate verbs, remove -ate and add -able

Several verbs ending in -ate form the adjective by dropping -ate and taking -able: communicate → communicable, appreciate → appreciable, educate → educable, demonstrate → demonstrable, tolerate → tolerable, navigate → navigable.

Situations That Call for -ible

Guideline 1: Use -ible when the remaining base is not a full English word

If taking off the suffix leaves a fragment rather than a normal standalone word, -ible is often the spelling you need. Common examples include tang-ible, gull-ible, fung-ible, fall-ible, elig-ible, cred-ible, vis-ible, terr-ible, poss-ible, horr-ible, feas-ible, ed-ible, and aud-ible.

Guideline 2: Look for bases connected with -ns or -miss

Several -ible words belong to families with forms such as response, sense, defense, permit, and admit: responsible, sensible, defensible, comprehensible, permissible, admissible.

Guideline 3: Soft c and soft g often point to -ible

Some words use -ible because that ending helps preserve the soft c or g sound. Examples include intelligible, eligible, negligible, legible, deducible, reducible, invincible, and forcible.

Guideline 4: Endings such as -pt and -ct may take -ible

Words with bases ending in sounds like -pt or -ct often use -ible: digestible, convertible, destructible, corruptible, contemptible. This is not absolute, though. Predictable, detectable, and respectable all use -able.

Frequently Used -able Words

Workable, washable, vulnerable, viewable, variable, valuable, usable, understandable, transferable, tolerable, teachable, sustainable, suitable, solvable, seasonal, searchable, returnable, respectable, repairable, renewable, remarkable, reliable, regrettable, refundable, recognizable, reasonable, readable, quotable, questionable, programmable, profitable, preventable, predictable, preferable, playable, perishable, payable, operable, obtainable, noticeable, negotiable, movable, miserable, memorable, measurable, manageable, likeable, laughable, justifiable, improbable, imaginable, honorable, forgettable, foreseeable, favorable, fashionable, expandable, excusable, erasable, enjoyable, durable, drinkable, desirable, dependable, definable, debatable, curable, considerable, conceivable, comparable, comfortable, changeable, capable, breakable, believable, avoidable, applicable, allowable, agreeable, affordable, advisable, admirable, adaptable, achievable, acceptable.

Frequently Used -ible Words

Visible, terrible, tangible, susceptible, sensible, risible, reversible, responsible, reproducible, reprehensible, reducible, possible, plausible, permissible, perceivable, ostensible, negligible, legible, irresistible, irascible, invisible, invincible, intelligible, intangible, insensible, inflexible, infallible, inedible, indestructible, indelible, incredible, incorrigible, inaudible, inadmissible, impossible, implausible, illegible, horrible, gullible, forcible, flexible, feasible, fallible, expressible, exhaustible, eligible, edible, divisible, discernible, digestible, destructible, defensible, deductible, crucible, credible, convertible, contemptible, comprehensible, compatible, combustible, collapsible, audible, admissible, accessible.

Problem Spellings and Exceptions

• Accessible: The correct spelling always uses -ible. It is also a very commonly misspelled word.
• Digestible: This word takes -ible even though digest is a complete English word.
• Flexible: The spelling is always -ible, although flex can stand on its own.
• Contemptible / Contemptable: The accepted spelling is contemptible; contemptable is not standard.
• Discernible: This is another exception, because discern is a complete word but the adjective still ends in -ible.
• Collectable / Collectible: Both forms are used. Collectible is especially common as a noun meaning an item worth collecting, while collectable fits the usual -able pattern.

Connected Forms: -ably/-ibly and -ability/-ibility

Once you know whether the adjective uses -able or -ible, the related adverb and noun forms usually follow the same spelling pattern:

• Accessible → accessibly → accessibility
• Responsible → responsibly → responsibility
• Flexible → flexibly → flexibility
• Reasonable → reasonably → reasonability (though reasonableness is more common)
• Comfortable → comfortably → comfortability

In other words, learning the adjective gives you the spelling key for -ably/-ibly and -ability/-ibility forms as well.

Ways to Remember the Spellings

1. Start with the complete-word test: If the ending is removed and a normal English word remains, -able is often the answer. If only a fragment remains, try -ible first.
2. Treat -ible as the smaller list. Since there are far fewer -ible words, it is practical to learn the most common ones and use -able as your default for the rest.
3. Check related -tion and -sion words. Words with -tion relatives often lean toward -able, as in information → informable, although informative is the usual word. Words with -sion relatives often lean toward -ible, as in permission → permissible and comprehension → comprehensible.
4. Use a dictionary when the pattern fails. Some words are exceptions, and a quick lookup is the safest choice when you are unsure.

Final Takeaway

The difference between -able and -ible can be annoying, but it follows enough patterns to be learnable. Use -able as the normal spelling, watch for the common signals that point to -ible, and memorize the shorter set of frequent -ible words. Alongside other core spelling rules, these habits will help you choose the right ending more reliably.