Origins
The suffix '-able' is one of the most productive adjective-forming suffixes in English.βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ It attaches to verbs (and occasionally nouns) to form adjectives meaning 'capable of being [verbed],' 'worthy of [verbing],' 'fit for,' or 'liable to.' 'Read > readable' (capable of being read), 'love > lovable' (worthy of love), 'accept > acceptable' (worthy of acceptance), 'break > breakable' (liable to break), 'believe > believable' (worthy of belief), 'forget > forgettable' (liable to be forgotten).
The suffix descends from Latin '-Δbilis,' itself a compound: the element *-dhlo- or *-dhli- from Proto-Indo-European (an instrumental / adjectival suffix seen elsewhere in English words like 'needle' and 'saddle') combined with the vowel of the Latin first conjugation. Latin 'amΔbilis' (lovable, from 'amΔre,' to love), 'laudΔbilis' (praiseworthy), 'potΔbilis' (drinkable), 'mΕ«tΔbilis' (changeable), 'probΔbilis' (provable, believable), 'notΔbilis' (noteworthy). In Latin, '-Δbilis' was fully productive and formed adjectives from any first-conjugation verb.
Latin also had '-ibilis' (with -i- instead of -a-), which attached to verbs of the third conjugation. English inherited this as '-ible' in certain Latin borrowings: 'edible,' 'visible,' 'horrible,' 'terrible,' 'possible,' 'impossible,' 'legible,' 'audible,' 'accessible,' 'credible,' 'divisible,' 'feasible,' 'flexible,' 'gullible,' 'incredible,' 'indelible,' 'invisible,' 'irresistible,' 'negligible,' 'permissible,' 'reversible,' 'sensible,' 'susceptible,' 'tangible.' These are all Latin borrowings, not English productive coinages. English speakers generally do not coin new '-ible' words; '-able' is the living, productive suffix.
Middle English
Old French inherited both Latin suffixes as '-able' and '-ible.' Middle English borrowed heavily from French, importing many '-able' and '-ible' adjectives: 'acceptable,' 'admirable,' 'affable,' 'amiable,' 'capable,' 'comfortable,' 'convenient (via -ient, not -able),' 'durable,' 'honourable,' 'noble,' 'profitable,' 'reasonable,' 'stable,' 'suitable,' 'valuable,' 'venerable,' 'veritable.'
From the fifteenth and sixteenth centuries onward, English speakers began attaching '-able' freely to native verbs: 'readable' (1570s), 'lovable' (c. 1340), 'breakable' (1560s), 'drinkable' (1571), 'eatable' (1483), 'speakable,' 'workable' (1570s). This made '-able' an extraordinarily productive suffix capable of creating new words on demand. Today any verb can potentially take '-able': 'googleable,' 'tweetable,' 'scannable,' 'clickable,' 'installable,' 'downloadable,' 'uploadable,' 'searchable,' 'relatable.'
Spelling rules for '-able' are regular. Silent '-e' at the end of a base is usually dropped ('love > lovable,' 'believe > believable,' 'desire > desirable,' 'value > valuable'), though it is sometimes retained to preserve pronunciation of a preceding soft 'c' or 'g' ('notice > noticeable,' 'manage > manageable,' 'change > changeable,' 'replace > replaceable,' 'trace > traceable'). Consonants after a short stressed vowel are usually doubled ('forget > forgettable,' 'regret > regrettable,' 'commit > committable'). Final '-y' becomes '-i-' ('vary > variable,' 'apply > appliable' β though 'applicable' is the established form from a different stem).
Latin Roots
The distinction between '-able' and '-ible' often confuses English spellers because both sound identical. A rough guide: '-able' is used with native English roots, French-derived bases, and modern productive coinages; '-ible' appears only in older Latin borrowings with specific Latin verb stems. Some words have both spellings attested: 'collectable' / 'collectible' (both valid, with 'collectible' more common in American English for 'something worth collecting'). When in doubt, '-able' is the safe productive choice.
Pronunciation is /ΙbΙl/ in both British and American English, with the suffix unstressed and the schwa reduced. Stress almost never falls on '-able.' In some words the preceding syllable is stressed: 'com-PAR-a-ble,' 'in-VIN-ci-ble,' 'ac-CEPT-a-ble.'
The meaning of '-able' is predictable but has subtle variations. Most common is 'capable of being X-ed' (readable = capable of being read, breakable = capable of being broken, washable = capable of being washed). Sometimes the meaning is 'worthy of being X-ed' (lovable = worthy of love, admirable = worthy of admiration, noteworthy). Sometimes it is 'liable to X' or 'prone to X' (perishable = liable to perish, breakable = prone to breaking). Sometimes it is active rather than passive: 'comfortable' (causing comfort, originally 'capable of comforting'), 'agreeable' (pleasant to agree with), 'reliable' (capable of being relied on), 'suitable' (fit for a purpose).
Cultural Impact
An unusual feature of '-able' is that it has become so productive that it functions almost independently as a semantic unit. The word 'able' itself exists as a free-standing adjective (from the same Latin root 'habΔre,' to have, via 'habilis,' 'handy'), and speakers intuitively feel that '-able' means 'able to be X-ed.' This is etymologically a coincidence β Latin '-Δbilis' and Latin 'habilis' (from 'habΔre') are related but the suffix does not historically derive from the free word β but the folk-etymological link reinforces the transparency of the suffix.
Representative '-able' adjectives include: acceptable, accessible (-ible), achievable, adaptable, adjustable, admirable, adorable, affable, affordable, agreeable, amiable, amenable, applicable, approachable, appreciable, arguable, attainable, available, avoidable, bearable, believable, breakable, calculable, capable, changeable, charitable, clearable, comfortable, commendable, compatible (-ible), comparable, conceivable, considerable, controllable, countable, credible (-ible), curable, debatable, defensible (-ible), deliverable, dependable, desirable, digestible (-ible), dispensable, disposable, divisible (-ible), doable, drinkable, drivable, durable, eatable, edible (-ible), educable, enduring (not -able), enjoyable, equitable, excusable, exchangeable, executable, expandable, explainable, extendable, fashionable, favourable, feasible (-ible), fixable, flexible (-ible), foreseeable, forgettable, forgivable, formidable, fortunate (not -able), friable, habitable, honourable, hospitable, huggable, imaginable, imitable, immovable, impassable, impeccable, implacable, impossible (-ible), impracticable, improbable, inapplicable, inaudible (-ible), incalculable, incapable, incompatible (-ible), incomprehensible (-ible), inconceivable, inconsolable, incredible (-ible), incurable, indelible (-ible), indescribable, indestructible (-ible), indisputable, indistinguishable, inedible (-ible), inevitable, inexplicable, inextricable, inflammable, inflexible (-ible), insatiable, invaluable, invincible (-ible), invisible (-ible), jammable, justifiable, knowable, laughable, legible (-ible), liable, likable / likeable, livable, lovable, manageable, marketable, marriageable, measurable, memorable, miserable, movable / moveable, navigable, negligible (-ible), negotiable, noticeable, observable, obtainable, palatable, passable, payable, peaceable, penetrable, perishable, permissible (-ible), pliable, portable, possible (-ible), practicable, predictable, preventable, printable, probable, profitable, programmable, provable, punishable, quantifiable, quotable, reachable, readable, reasonable, recognisable, recyclable, reliable, remarkable, removable, renewable, repairable, replaceable, reputable, resistible (-ible), respectable, responsible (-ible), reusable, reversible (-ible), salvageable, scannable, searchable, serviceable, sizable, stable, suitable, survivable, susceptible (-ible), sustainable, taxable, teachable, tenable, terrible (-ible), tolerable, touchable, traceable, tractable, trainable, transferable, transportable, treatable, tremble (not -able), trustable, unable, uncountable, understandable, unstoppable, usable, valuable, venerable, verifiable, viable, visible (-ible), voluble, vulnerable, washable, wearable, winnable, workable, worthwhile (not -able). Productive modern: bloggable, clickable, computable, downloadable, emailable, googleable, hackable, installable, printable, programmable, publishable, rentable, scannable, streamable, tweetable, uploadable, viewable.