What this is
French has three regular present-tense verb families. You already know -er, the largest one. This is the first half of the second family: -ir verbs that insert -iss- across the plural. finir (to finish), choisir (to choose), and réussir (to succeed) all belong here, and once you have the pattern, dozens of other -ir verbs — grandir, réfléchir, obéir, rougir, grossir, maigrir, vieillir, remplir — conjugate exactly the same way.
There’s a second -ir family that does not take -iss- (partir, dormir, sortir), covered in the next concept. The two families look identical in the infinitive — you can’t tell which one a new verb belongs to just by looking at “-ir” — so this concept exists partly to give you the one test that actually works.
The rule
Drop -ir from the infinitive to get the stem. finir → fin-. Then add:
| ending | finir | choisir | réussir | |
|---|---|---|---|---|
| je | -is | finis | choisis | réussis |
| tu | -is | finis | choisis | réussis |
| il/elle/on | -it | finit | choisit | réussit |
| nous | -issons | finissons | choisissons | réussissons |
| vous | -issez | finissez | choisissez | réussissez |
| ils/elles | -issent | finissent | choisissent | réussissent |
The singular row is short and unremarkable — it’s the plural row that names this family. That -iss- block appearing out of nowhere between the stem and the ending is the entire identity of this conjugation pattern.
Other everyday verbs that follow it exactly: grandir (to grow up), réfléchir (to think), obéir (to obey), rougir (to blush), grossir (to gain weight), maigrir (to lose weight), vieillir (to age), remplir (to fill), and many more — choisir/réfléchir/finir aren’t a closed set, they’re a sample of a genuinely large family.
Two verbs pair with a following infinitive using their own preposition, which you just have to know per verb: finir de + infinitive (“to finish doing”), réussir à + infinitive (“to succeed in doing” / “to manage to do”). réussir also takes a direct object with no preposition when the thing succeeded at is a noun rather than an action: réussir un examen, “to pass an exam.”
Why it works this way
The -iss- infix isn’t decoration — historically it’s a trace of an earlier form of the verb that showed up throughout the conjugation and later got worn down to nothing in the singular, surviving only where the ending that followed it protected it from being dropped. You don’t need the history to use the rule, but it explains why the split feels so arbitrary from the outside: it’s not a spelling convention, it’s a fossil.
Practically, this means the plural is where the verb’s true family reveals itself. If you only ever heard someone speak in the singular, you’d have no way to know whether “il finit” belongs to this family or the bare-stem family next door — the two sound completely different in the plural (finissons vs. the next concept’s dormons) but identical-ish in structure in the singular.
Edge cases
The three singular forms sound identical
je finis, tu finis, and il finit are spelled with three different endings but pronounced as exactly the same sound — /fini/. There is no audible difference between “I finish,” “you finish,” and “he finishes” until the sentence tells you who the subject is some other way (the pronoun itself, spoken clearly, is doing all the work). This is normal and not a sign you’re mishearing something.
The -iss- test is how you identify the family
When you meet a new -ir verb and need to know which pattern it follows, check the nous form. If it takes -issons, it’s this family. If it doesn’t — if the plural just adds -ons directly onto a shortened stem — it’s the other -ir family, the one built on partir, dormir, and sortir, which the next concept covers. There’s no way to guess from the infinitive alone; the plural is the only reliable signal.
What English speakers get wrong here
The most common mistake is trying to shortcut the memorization by pattern-matching from -er verbs, which produces “finis, finis, finis, finons, finez, finent” — a plausible-looking but wrong paradigm that drops the -iss- entirely. The -iss- has to be memorized as belonging to the plural, not derived from the singular.
The second mistake is the reverse: once a learner notices -iss- exists, they start inserting it into the singular too — “je finiss,” “tu finiss” — which never happens. The infix is a plural-only feature; the singular stays short.
The third is choosing the wrong preposition after finir or réussir, usually by translating English literally. “I finish to eat” doesn’t work in English and neither does its mirror image in French: it’s finir de manger, never finir à manger. Each verb’s preposition has to be learned as part of the verb, not derived from what feels natural.