Préfixes et suffixes
French has an enormously productive system of word-formation. Once you internalize the common préfixes and suffixes, you can guess the meaning AND the part of speech of thousands of words you've never seen. A noun ending in -tion is feminine and abstract: information, création, explication. An adjective ending in -able means 'capable of being X-ed': mangeable, lisible, acceptable. A noun in -eur/-euse is the agent of a verb: chanteur/chanteuse (singer), vendeur/vendeuse (seller). A prefix re-/ré- repeats the action: refaire (redo), revoir (see again). A prefix in-/im-/il-/ir- negates: impossible, illégal, irréel. This lesson is the cheat sheet — the productive affixes that let you decode and even invent French words.
Negation prefixes — in-, im-, il-, ir-, dé-/dés-, mé-
The in- prefix (and its variants im- before m/p/b, il- before l, ir- before r) negates an adjective: possible → impossible; lisible → illisible (illegible); réel → irréel (unreal); utile → inutile (useless); complet → incomplet; buvable → imbuvable (undrinkable). The variant is purely phonetic — match the consonant. This works on hundreds of adjectives. The prefix non- also negates, often with a hyphen: non-fumeur (non-smoker), non-violence. Different from negation, dé-/dés- undoes an action — it's the French 'un-' or 'de-': faire → défaire (undo); monter → démonter (dismantle); habiller → déshabiller (undress); organiser → désorganiser. dés- appears before vowel: dés-organiser, dés-armer (disarm), dés-engager. Finally, mé-/més- carries 'badly' or 'wrongly': content → mécontent (displeased); comprendre → se méprendre (misunderstand oneself); estimer → mésestimer (underestimate). Less productive but recognizable. Master these and you double the adjective vocabulary you can recognize.
Repetition and intensification — re-/ré-, sur-, super-, hyper-, ultra-
re- (or ré- before vowels and sometimes for emphasis) means again — extraordinarily productive: faire → refaire; voir → revoir; lire → relire; écrire → réécrire; commencer → recommencer (start again). It can also mean 'back': rentrer = come back home; revenir = come back. With many verbs, re- is so freely added that French uses it like a particle. sur- = above / over (excess): chargé → surchargé (overloaded); estimer → surestimer (overestimate); peuplé → surpeuplé (overpopulated); prendre → surprendre (catch by surprise — etymologically 'take from above'). The casual intensifiers super-, hyper-, and ultra- stack onto adjectives in informal speech: super sympa, hyper bon, ultra rapide, mega cool. They're spelled either solid or with hyphen: super-marché (supermarket — solid), but most casual uses are written separately: C'est super bien. = It's super good. Slightly opposite, sous- = under: estimer → sous-estimer (underestimate); payer → sous-payer (underpay); alimenté → sous-alimenté (undernourished).
Position and time — pré-, post-, anti-, pro-, co-, ex-
pré- = before: vu → prévu (foreseen); dire → prédire (predict); histoire → préhistoire; chauffé → préchauffé (preheated). post- = after, less productive but appears in formal/technical: post-guerre (post-war), post-moderne. anti- = against: antibiotique, anticonformiste, antidémocratique; with hyphen often: anti-âge, anti-stress. pro- = in favor of: pro-européen, pro-démocratie. co- = together, with: collaborer, coopérer, co-auteur, colocataire (roommate — co-tenant). ex- = former: ex-président, ex-femme (ex-wife), ex-petit ami. Almost always hyphenated. Time-related, avant- = before: avant-hier (day before yesterday), avant-bras (forearm), avant-garde. après- = after: après-midi (afternoon), après-demain (day after tomorrow), après-guerre. These prefixes are mostly transparent if you know the root.
Noun-forming suffixes — -tion, -sion, -ment, -ité, -age, -isme
These suffixes turn verbs and adjectives into abstract nouns. -tion / -sion / -ation form a feminine noun from a verb, naming the action or its result: créer → création; informer → information; décider → décision; construire → construction; expliquer → explication. Always feminine. Massive overlap with English -tion — the catch is the gender (feminine) and the meaning (often the act, sometimes the result). -ment forms a masculine noun naming a process or thing: changer → changement; développer → développement; mouvoir → mouvement; bâtir → bâtiment (building). All masculine. (Note: -ment also forms adverbs from adjectives — context disambiguates.) -ité forms a feminine abstract noun from an adjective, like English -ity: réel → réalité; possible → possibilité; rapide → rapidité; égal → égalité. Always feminine. -age forms a masculine noun, often an action or its result: passer → passage; laver → lavage (washing); stocker → stockage. Almost always masculine — exceptions like plage (beach) and image (image) are rare. -isme = ideology / movement (masculine): capitalisme, socialisme, réalisme, journalisme. -iste = adherent / professional (m./f.): un/une journaliste, un/une artiste, un/une dentiste.
Agent and result suffixes — -eur/-euse/-trice, -ier/-ière, -aine
The most productive agent suffix is -eur (m.) / -euse (f.): derived from a verb, names the doer: chanter → chanteur/chanteuse (singer); vendre → vendeur/vendeuse; danser → danseur/danseuse; travailler → travailleur/travailleuse; menteur/menteuse (liar). For Latinate / professional / scientific terms, the feminine is often -trice: acteur/actrice; directeur/directrice; lecteur/lectrice (reader); auteur/autrice (author — recent, alongside older auteure); administrateur/administratrice. The choice of -euse vs -trice depends on the root: -trice for Latin verbs ending in -ateur/-iteur, -euse elsewhere. The suffix -ier (m.) / -ière (f.) marks profession or container: boulangerie has boulanger/boulangère (baker); policier/policière (police officer); infirmier/infirmière (nurse); also containers: soupière (soup tureen), sucrier (sugar bowl). The suffix -aine turns a number into an approximate round amount, feminine: dix → dizaine (about ten); vingt → vingtaine (about twenty); cent → centaine (about a hundred); douze → douzaine (a dozen). Une vingtaine de personnes = about twenty people. The suffix -ée (feminine) marks duration/contents: journée (a day's worth), soirée, matinée, année — distinct from the punctual jour, soir, matin, an.
Adjective-forming suffixes — -able/-ible, -eux/-euse, -if/-ive, -al
-able / -ible = capable of being X-ed (passive potential), like English -able: mangeable (eatable), lisible (readable), acceptable, incroyable (incredible — in- + croy- + -able), invisible, possible. Identical in gender. -eux (m.) / -euse (f.) = full of, characterized by: courage → courageux (courageous); danger → dangereux; paresseux (lazy, from paresse); ennuyeux (boring); chanceux (lucky); précieux (precious, -ieux variant). -if (m.) / -ive (f.) = having the quality of: actif/active, positif/positive, créatif/créative, agressif/agressive, massif/massive. -al (m.) / -ale (f.), plural masculine -aux: national/nationaux, principal/principaux, mondial/mondiaux, génial/géniaux. Note the irregular plural: un journal → des journaux. -aire = related to: bancaire (banking-related), universitaire (university-related), populaire, militaire, alimentaire (food-related). Same form for both genders. With these you can decode an adjective's likely meaning AND know how to form its feminine and plural.
Quick recap
(1) Negation: in-/im-/il-/ir- for adjectives (impossible); dé-/dés- for undoing actions (défaire); mé- for badly (mécontent); non- for nouns (non-fumeur). (2) Intensification & repetition: re-/ré- = again (refaire); sur- = over- (surcharger); sous- = under- (sous-estimer); super-/hyper-/ultra- = casual intensifiers. (3) Time/position: pré- before, post- after, anti- against, pro- for, co- with, ex- former, avant-/après- before/after. (4) Nouns from verbs/adjectives: -tion/-sion (f.), -ment (m.), -ité (f.), -age (m.), -isme (m.), -iste (m./f.). (5) Agents: -eur/-euse or -eur/-trice; -ier/-ière for trades; -aine for round numbers. (6) Adjectives: -able/-ible (capable of); -eux/-euse (full of); -if/-ive (having quality of); -al (relating to, plural -aux); -aire (related to). With this map you can decode 80% of unknown French vocabulary on first sight.
