adjective + infinitive, à vs de.
Adjectives sort into two fixed vocabulary groups — feelings and dispositions — plus a third group where the preposition follows the shape of the sentence rather than the adjective itself. That third piece explains why several adjectives labeled “exceptions” elsewhere aren’t exceptions at all.
- Je suis content de te voir.
- Je suis prêt à partir.
- C’est facile à faire.
- Il est facile de faire ça.
Look at the last two lines above. Same adjective, facile, opposite preposition. No meaning-based rule explains that — but a structural one does, and it’s the key to this whole topic. Throughout this guide, de and à mark which category an example belongs to, so the pattern stays visible even when the table below it doesn’t.
Part 1
Feelings take de
When a personal subject — je, il, elle, nous — is reporting an emotional or physical reaction to the action, the adjective takes de. This group is genuinely just a vocabulary list: there’s no deeper structure to derive, only a consistent semantic thread of “how the subject feels about this.”
| Adjective | Meaning | Example |
|---|---|---|
| content | happy | Je suis content de te voir. |
| heureux | happy | Il est heureux de réussir. |
| triste | sad | Elle est triste de partir. |
| fier | proud | Il est fier de gagner. |
| surpris | surprised | Nous sommes surpris d’apprendre ça. |
| fatigué | tired | Je suis fatigué de travailler. |
| soulagé | relieved | Elle est soulagée de savoir. |
| ravi | delighted | Il est ravi de te rencontrer. |
| désolé | sorry | Je suis désolé d’être en retard. |
| ennuyé | bored / annoyed | Je suis ennuyé de répéter ça. |
| horrifié | horrified | Il est horrifié de voir ça. |
| effrayé | frightened | Elle est effrayée de sortir seule. |
| inquiet | worried | Je suis inquiet de ne pas avoir de nouvelles. |
| lassé | weary | Je suis lassé d’entendre ces excuses. |
Quick test: if the English can be rephrased as “I feel [adjective] that I do this,” you’re in this group. Je suis fatigué de travailler ← “I feel tired that I work [this much].” This test is reliable here because the subject in both languages is a person having a reaction — there’s no structural ambiguity to trip it up.
Part 2
Disposition takes à
A second group of adjectives describes a personal subject’s disposition: how ready, inclined, quick, or accustomed they are to doing something. Like the “feelings” group, this is a fixed vocabulary list — these adjectives don’t alternate with de depending on sentence structure, they simply take à.
| Adjective | Meaning | Example |
|---|---|---|
| prêt | ready | Je suis prêt à partir. |
| enclin | inclined | Il est enclin à exagérer. |
| disposé | willing | Je suis disposé à t’aider. |
| habitué | accustomed | Je suis habitué à travailler tôt. |
| lent | slow | Il est lent à réagir. |
| rapide | fast | Elle est rapide à apprendre. |
| habile | skilled | Il est habile à négocier. |
| prompt | prompt, quick | Elle est prompte à répondre. |
| déterminé | determined | Il est déterminé à réussir. |
Déterminé is worth flagging: on meaning grounds it sits near obligé and sûr (Part 4), which take de. It doesn’t — it belongs here instead, as a disposition word. There’s no way to predict this from meaning alone; it’s simply one to memorize.
Part 3
Quality adjectives: the real rule is about the subject, not the adjective
This is the group that includes facile, difficile, important, nécessaire, possible — words that describe a property of the action itself rather than anyone’s feelings about it. The preposition here isn’t a fixed property of the adjective; it depends on which of two sentence structures you’re building. Watch what happens to the same adjective under both:
IMPERSONAL IL + DE
Il est facile de résoudre ce problème.”It is easy to solve this problem” — new information, introduced by empty “il.”Il est nécessaire de partir tôt.It is necessary to leave early.
CONCRETE SUBJECT + À
Ce problème est facile à résoudre.The problem — already on the table — is easy [to solve it].Ce texte est difficile à comprendre.This text is hard [to understand it].
The mechanism: in the à pattern, the grammatical subject (ce problème) is the logical object of the infinitive — it’s the thing being solved. French marks that relationship with à and drops the object pronoun that would otherwise be needed (résoudre, not le résoudre). In the de pattern, “il” is empty — a grammatical placeholder — and the real content is the whole infinitive clause, introduced by de. These are two different sentences built around the same adjective, not two meanings of the adjective.
This is also why the popular English test — “it is [adjective] to do this” — can’t reliably tell you which preposition to use: English collapses both French structures into the same phrasing. Il est facile de résoudre ce problème and Ce problème est facile à résoudre both translate as “it’s easy to solve this problem.” The English gloss is genuinely ambiguous between them; only the French sentence’s own shape decides.
So why does nécessaire “always” take de? Not because necessity is a special meaning category — but because “?Ce rapport est nécessaire à lire” is odd in a way that “Ce rapport est facile à lire” isn’t. Some quality adjectives resist being restated with a concrete subject as the implied object; nécessaire, important, essentiel, urgent are members of that lexically-restricted set. That restriction has to be memorized per word — but it’s a much narrower, more honest fact than “necessity words are exceptions to the à rule.”
Adjectives that readily form both patterns
| Adjective | Il est … de | [Subject] est … à |
|---|---|---|
| facile | Il est facile de faire ça. | C’est facile à faire. |
| difficile | Il est difficile de le convaincre. | Il est difficile à convaincre. |
| agréable | Il est agréable de te voir. | Cette chaise est agréable à regarder. |
| possible | Il est possible de terminer aujourd’hui. | Ce travail est possible à terminer aujourd’hui. |
Adjectives that resist the à pattern (memorize as de-only)
| Adjective | Meaning | Example |
|---|---|---|
| nécessaire | necessary | Il est nécessaire de partir tôt. |
| essentiel | essential | Il est essentiel de comprendre ça. |
| important | important | Il est important de vérifier. |
| urgent | urgent | Il est urgent d’agir. |
Part 4
Obligation or certainty takes de
These describe a personal subject’s state of confidence or obligation rather than a task’s quality — closer in spirit to Part 1’s feelings than to Part 3’s quality words, but not emotional enough to belong there either. They form their own small, fixed group.
| Adjective | Meaning | Example |
|---|---|---|
| obligé | obliged | Je suis obligé de partir. |
| sûr | sure | Il est sûr de gagner. |
| certain | certain | Je suis certain d’avoir raison. |
| capable | capable | Elle est capable de réussir. |
Capable belongs here, not with the necessity words in Part 3 — capability is a personal attribute, not a property of the task, even though both groups happen to take de.
Part 5
Preposition can change the meaning
A handful of adjectives can go either way, and here the choice really does change what’s being said — because it’s choosing between the two structures from Part 3, not flipping a coin.
| Adjective | With à (object quality) | With de (impersonal statement) |
|---|---|---|
| bon | Bon à manger — good to eat, describing the food | Bon de savoir — good [in general] to know this |
| mauvais | Mauvais à dire — bad, describing the thing said | Mauvais de mentir — lying [as an act] is bad |
| agréable | Agréable à regarder — pleasant, describing the object | Agréable de vous voir — pleasant [for me] to see you |
| désagréable | Désagréable à porter — unpleasant to wear | Désagréable de vous déranger — it’s unpleasant [for me] to disturb you |
| utile | Utile à savoir — useful for a specific person to know | Utile de savoir — useful to know, in general |
Note that agréable and désagréable are not fixed à words, despite how they’re sometimes listed — they follow exactly the Part 3 alternation, like facile and difficile.
Part 6
Decision framework
- Is the subject a person reporting a feeling? (je, il, elle… + emotion word) → de. Check the Part 1 list.
- Is the subject a person describing their own readiness, speed, or habit? → à. Check the Part 2 list.
- Is the subject a person expressing confidence or obligation? (sûr, certain, obligé, capable) → de.
- Otherwise, are you describing a quality of a task or object? Ask which sentence you’re building:
- Starting from empty il, introducing the action as new information → de.
- Starting from a concrete subject that is the logical object of the infinitive → à.
- Does the adjective resist the à-pattern? nécessaire, essentiel, important, urgent — default to de regardless of structure.
Part 7
Practice
Fill each blank with à or de.
1. Je suis prêt partir.
2. Il est fatigué travailler.
3. C’est facile faire.
4. Il est facile faire ça.
5. Elle est contente te voir.
6. Il est nécessaire vérifier.
7. Je suis déterminé réussir.
8. Ce livre est agréable lire.
9. C’est agréable te rencontrer.
10. Il est sûr gagner.
11. Tu es habitué conduire à gauche.
Answers and reasoning
1. à — disposition word, Part 2, fixed.
2. de — personal feeling, Part 1.
3. à — “ce” stands in for a concrete, already-known thing being made; object-of-infinitive structure.
4. de — empty “il,” introducing “ça” as new information — same adjective as #3, different structure.
5. de — personal feeling, Part 1.
6. de — nécessaire resists the à-pattern; memorize as de-only.
7. à — déterminé is a disposition word despite its meaning suggesting otherwise.
8. à — “ce livre” is the object of “lire” — object-of-infinitive structure.
9. de — “c’est” here is impersonal, introducing “te rencontrer” as the point being made — not the object-of-infinitive pattern, even though it looks similar to #8 on the surface.
10. de — certainty word, Part 4.
11. à — habitué, disposition word, Part 2.
Summary
- Two vocabulary lists are genuinely fixed and must be memorized as words: personal feelings (de) and personal dispositions (à).
- For quality adjectives, the preposition usually follows sentence structure, not the adjective’s meaning: empty il + new information → de; concrete subject as the logical object → à.
- A short list of quality adjectives (nécessaire, essentiel, important, urgent) resist the à-structure and default to de regardless — that resistance is the real, narrow exception worth memorizing, not “necessity means de.”
- When the English gloss “it is [adjective] to…” doesn’t resolve it, that’s expected: English can’t distinguish the two French structures, so the ambiguity isn’t a gap in your knowledge — it’s a gap in the translation test.
