Formation: the future's stem, the imperfect's endings
Use a future stem ending in -r- and add the imperfect endings: -ais, -ais, -ait, -ions, -iez, -aient. For example, parler- + -ais gives parlerais. Per the Office québécois de la langue française's formation reference, regular -er and -ir verbs normally use the full infinitive as the future stem (nous aimerions, ils finiraient). In the OQLF’s alternative analysis, the radical excludes -er/-ir and is followed by e/i plus -rais; the two analyses must not be mixed. Most irregular -re verbs skip the extra vowel and attach the ending straight onto the infinitive minus its final e, which is why mettre gives mettrais rather than the metterais a learner might guess by analogy with the -er pattern.
A set of verbs replace the stem outright; simply tweaking it isn't enough for these. The OQLF's own conjugation table lists thirteen of them together, with no ranking by frequency, just an infinitive-to-stem pairing for each: acquérir becomes acquerr- (j'acquerrais), aller becomes ir- (j'irais), avoir becomes aur- (j'aurais), courir becomes courr- (je courrais), cueillir becomes cueiller- (je cueillerais), être becomes ser- (je serais), faire becomes fer- (je ferais), mourir becomes mourr- (je mourrais), pouvoir becomes pourr- (je pourrais), savoir becomes saur- (je saurais), tenir becomes tiendr- (je tiendrais), venir becomes viendr- (je viendrais), and voir becomes verr- (je verrais).
Spelling also shifts in predictable ways within the regular pattern: verbs like acheter or peser turn their stem's e into è (j'achèterais, nous pèserions), verbs ending in -oyer or -uyer swap y for i (je nettoierais), and a small set of -eler/-eter verbs (appeler, jeter, and their derivatives) double the final consonant instead (elle appellerait). Traditional spelling also doubles consonants in some other -eler/-eter verbs. The 1990 revised forms generally use è, while appeler, jeter and their derivatives retain the doubled consonant. Both spelling systems are accepted.
Mood or tense? The classification most courses never mention
French grammar traditionally sorted the conditional in with the true moods, subjonctif and impératif, treating it as a separate way of framing a statement, not simply another point on the timeline. Plenty of standard teaching references still classify it that way: Lawless French, cited elsewhere in this article for its habitual-past distinction, sorts the conditional as its own mood, built around hypothetical meaning rather than a fixed place on the timeline. The Office québécois de la langue française takes the opposite position. Per its own overview page: "longtemps présenté comme un mode, le conditionnel est maintenant considéré par la majorité des linguistes et grammairiens comme un temps du mode indicatif," long presented as a mood, the conditional is now considered by most linguists and grammarians to be a tense within the indicative mood. The OQLF illustrates the structural relationship through the endings: the -r- is the same marker the simple future carries, and the six endings that follow are identical to the imperfect's, which makes the conditional look, structurally, like a close relative of two indicative tenses instead of an independent grammatical category.
Neither position erases the conditional's hypothetical, modal side, and the OQLF is explicit that the line between mood and tense gets blurry here precisely because several indicative tenses (the future and the imperfect among them) already carry modal shades of their own, without anyone proposing to reclassify those as separate moods. Spanish's condicional simple has also prompted debate over its classification: the RAE classifies it as an indicative tense, following a long-standing discussion over whether it constitutes a separate mood. French's own subjunctive skips that argument entirely; it stays sorted with impératif as a separate mood in the OQLF’s classification.
The si rule: why the if-clause can never take the conditional
The OQLF gives common hypothetical patterns in which the verb directly governed by conditional si is indicative present or past, rather than future or conditional. These are useful models, not an exhaustive list of every combination. Si + present can pair with a future-tense consequence (si Mélanie oublie mon anniversaire, je lui pardonnerai). Si + imperfect pairs with a conditional-present consequence describing something that could still happen (si Mélanie oubliait mon anniversaire, je lui pardonnerais, not si Mélanie oublierait). Si + pluperfect can pair with a conditional present for a current hypothetical result, or with a conditional past for an unreal past result (si tu avais été attentif, je n'aurais pas eu besoin de répéter).
Putting the conditional directly after si is one of the errors French teachers correct most often in English-speaking learners, because both halves of a hypothetical sentence feel equally uncertain to a speaker in the moment, even though French uses different tense and mood patterns in the condition and its result. Spanish also distinguishes common open, present-hypothetical and unreal-past conditions, with mixed pairings possible as well: the imperfect and pluperfect that appear in a French si-clause are both indicative forms, while the equivalent Spanish protases switch into the imperfect or pluperfect subjunctive instead. These examples illustrate differing mood choices. Additional pairings exist in both languages. The plus-que-parfait sits one step further back than the pairings on this page, marking what was already done before the past moment being narrated.
The rule has two narrower exceptions, and both hinge on what si is actually doing in the sentence: not every si sets up a condition. The better-known one: when si introduces an indirect question, the conditional is fully correct on either side of it. Nous aimerions savoir si vous seriez disposée à entrer en fonction le mois prochain is a reported version of the direct question seriez-vous disposée...?, not a hypothesis, so the ban doesn't apply. The reliable test is substitution: a translation with "whether" helps identify interrogative si, where the conditional is allowed. An ordinary hypothetical "if" construction instead follows the tense restrictions just described; other si meanings must be considered separately. The second, rarer exception is concessive si, where the clause concedes a point without laying down a condition at all: per the OQLF, si l'on ne saurait affirmer hors de tout doute qu'il pleuvra, on peut assurément dire que le ciel sera couvert ("granted, no one can say for certain it will rain, but the sky will definitely be overcast") uses the conditional saurait in the concessive clause; pleuvra is inside its embedded complement. Here si means something closer to "granted that" than "if." French grammar sites commonly summarize the base rule with the rhyme les si n'aiment pas les rais, "the ifs don't like the -rais endings," a mnemonic that covers only the conditional si and says nothing about either exception.
Two more genuine uses, and the "would" trap
Outside hypotheticals, the conditional carries a real temporal job the OQLF calls the futur du passé, the future of the past: when a past-tense verb is followed by a conditional-tense verb, the conditional marks something that's future relative to that past moment, not future relative to now. Sara a appris hier que son frère l'accompagnerait uses accompagnerait to describe an event later than the past moment when Sara learned about it, even though the whole sentence is grammatically anchored in yesterday. The same substitution shows up in indirect reported speech: if the original statement used the future tense, quoting it indirectly after a past-tense verb converts that future into a conditional. François a affirmé qu'il ne voterait que selon sa conscience reports what was originally je ne voterai que selon ma conscience, with voterai becoming voterait purely because the reporting verb, a affirmé, sits in the past.
English "would" is a false-friend guide to when the conditional actually applies, and not a translation rule. "She would visit every summer" describes a repeated past habit, which French renders with the imperfect (elle rendait visite chaque été), not the conditional, despite the English wording looking identical to a hypothetical "would." The hypothetical and future-of-the-past senses of "would" can map onto the conditionnel; the habitual-past sense doesn't, which is the exact same trap Spanish's own conditional entry describes for that language's identical false-friend problem with "would."