Le Suffixe -able: capacité passive

The suffix -able (with its learned variant -ible) turns a verb into an adjective meaning "capable of being V-ed" — or sometimes simply "tending to V." It is one of the most productive adjective-forming suffixes in French, and one of the easiest for English speakers to use well, because the parallel with English -able is nearly perfect: mangeable / eatable, lisible / readable, imaginable / imaginable, faisable / doable.

This page covers how to form -able / -ible adjectives, when each variant is used, how to combine them with negative prefixes (in-, im-, il-, ir-) to form the huge family of negated forms (impardonnable, invraisemblable, illisible, irréparable), and a small set of cases where the suffix has drifted from its core "capable" meaning.

The core meaning: passive capability

A verb V combined with -able gives an adjective meaning "that can be V-ed" (passive capability) or, less commonly, "that V's, that tends to V" (active disposition).

• manger (eat) → mangeable — that can be eaten, edible
• boire (drink) → buvable — that can be drunk, drinkable
• faire (do, make) → faisable — that can be done, doable
• lire (read) → lisible — that can be read, legible
• voir (see) → visible — that can be seen, visible
• aimer (love) → aimable — likable, friendly, kind
• vivre (live) → vivable — livable

The passive reading is by far the most common. Une eau buvable is water you can drink; un problème faisable is a problem you can solve; une écriture lisible is handwriting you can read. The active reading ("that tends to V") survives mostly in a few high-frequency adjectives: aimable (friendly — "that tends to love / be loved"), agréable (pleasant — "that pleases"), raisonnable (reasonable — "that uses reason").

Formation: -able (default) vs -ible (learned)

French has two forms of the suffix, distributed by etymology and the verb class involved.

-able — the productive default

-able attaches to almost any verb, especially first-group (-er) verbs. It is the productive option: when modern French coins a new adjective of this type, it almost always uses -able.

For first-group verbs the formula is essentially mechanical: take the infinitive, drop the -er, add -able. Recycl|er → recyclable. Lav|er → lavable. Jet|er → jetable. The orthographic wrinkle is the same one you get throughout the -er conjugation: -ger verbs keep their e before -able to preserve the soft g (mang|er → mangeable, not mangable), and -cer verbs swap the c for ç to preserve the soft sound (prononc|er → prononçable, plac|er → plaçable).

-ible — the learned variant

-ible attaches to a smaller, mostly closed set of verbs, often from the second and third groups, and almost always from Latin learned vocabulary. It is the conservative option, and modern French does not usually coin new adjectives in -ible.

There is no shortcut for predicting -able vs -ible. Some verbs even take both, with slightly different meanings: recevable (admissible, of a legal claim) vs réceptible (rare). The safe strategy: treat -ible adjectives as a closed list of high-frequency items to memorize, and use -able productively for everything else.

Productivity: making new -able adjectives on the fly

-able is fully productive in modern French. Native speakers form new -able adjectives whenever convenient, especially in journalism, technology, and casual speech. Many of these are not yet in dictionaries but are perfectly natural.

For learners, this means if you need an -able adjective and you do not know one, build it. The risk of inventing a form that does not exist is low, and the resulting form is usually transparent and acceptable.

Negative forms: prefix + suffix

One of the most powerful uses of -able / -ible is in combination with the negative prefixes in-, im-, il-, ir- (see word-formation/prefix-in-im-il-ir). The combination gives an adjective meaning "incapable of being V-ed" — impardonnable (unforgivable), invraisemblable (implausible), illisible (illegible), irréparable (irreparable).

The choice between in-, im-, il-, and ir- is purely phonological:

• in- before a vowel or most consonants: invisible, incassable, inacceptable, inévitable.
• im- before b, m, p: impossible, imbattable, immangeable, imprévisible.
• il- before l: illisible, illimité, illégal.
• ir- before r: irréalisable, irréparable, irresponsable.

Agreement: like any other adjective

-able and -ible adjectives agree in gender and number like any other adjective. The masculine and feminine singular are identical (both end in -e); the plural simply adds -s.

A few drifted meanings

Several common -able / -ible adjectives have drifted away from the core "capable of being V-ed" sense and now have idiomatic meanings.

• aimable strictly should mean "lovable," but it usually means "friendly, kind, courteous" — the active "tending to please" sense. Soyez aimable = "Be kind / courteous."
• agréable means "pleasant," not "agreeable" in the sense of "willing to agree."
• sensible is a major false friend. It does not mean "sensible" (= reasonable, prudent). It means "sensitive" (emotionally tender) or "perceptible." French for English "sensible" is raisonnable or sensé.
• passable means "acceptable, just good enough" (from a school grade), not "passable" in the sense of "able to be passed (a road)."
• faisable is strictly "doable" — but it has a colloquial register and feels more casual than English "feasible." For a more formal register, réalisable is preferred.

Source-language note: English -able and -ible

English and French both inherited the suffix from Latin, and the mapping is unusually clean. Most English adjectives in -able / -ible have a French cognate with the same form and meaning: acceptable / acceptable, visible / visible, flexible / flexible, impossible / impossible. For English speakers, this is one of the cheapest pieces of French vocabulary to acquire — if you know the English word, the French is usually identical or near-identical.

Three traps to remember:

• The in-/im-/il-/ir- distribution. English happily writes unforgivable with un-; French uses impardonnable with im-. Always check the French prefix; never carry over English un-.
• Sensible. The biggest false friend. French sensible = English sensitive. English sensible = French raisonnable, sensé.
• Productivity is even higher in French. English will sometimes prefer "X-ed-up" or "fit for X-ing" where French uses a clean -able adjective. Reach for the -able form; it almost always exists.

Common Mistakes

Mistake 1: Using un- instead of in-/im-/il-/ir- for negation.

Mistake 2: Confusing sensible with English "sensible."

Mistake 3: Choosing the wrong variant (-able vs -ible).

Mistake 4: Wrong negative prefix for the following consonant.

Mistake 5: Forgetting to keep the soft consonant in -ger / -cer verbs.

Mistake 6: Forgetting agreement in the feminine plural.

Key takeaways

• -able (and its learned variant -ible) forms adjectives meaning "capable of being V-ed" — mangeable, lisible, faisable, imaginable.
• -able is highly productive; -ible is a closed list of mostly Latin-derived items.
• For first-group verbs the rule is mechanical: drop -er, add -able. -ger verbs keep the buffer e (mangeable); -cer verbs swap c for ç (prononçable) to preserve the soft sound.
• The negative prefixes in-, im-, il-, ir- combine freely with -able / -ible to form a vast inventory: impardonnable, inacceptable, illisible, irréparable. The prefix is selected phonologically.
• A handful of -able / -ible adjectives have drifted from the core sense — aimable (friendly), agréable (pleasant), sensible (sensitive, not "sensible"), passable (acceptable).
• English speakers can usually translate -able / -ible adjectives directly between the two languages — the suffix is genuinely shared. Watch the un- / in- distinction and the sensible false friend.