One of the most persistent challenges for French learners is knowing when to use à versus de before an infinitive. Consider these three common sentences:

Je suis content de te voir.
Je suis prêt à partir.
C’est facile à faire.

Why does one take de while the others take à? And why does an adjective like nécessaire—which appears to follow the same pattern as facile—take de instead?

This article provides a systematic framework for understanding these preposition choices. It explains the patterns that govern approximately 80% of cases and clearly identifies the exceptions that must be memorized individually.

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The Core Principle

The choice between à and de is determined by what the adjective is describing. While no single rule covers every case, a clear pattern emerges when examining the function of each preposition.

Preposition	Primary Function	Example
DE	Expresses the subject’s emotional or subjective response to the action	Je suis content de te voir.
À	Expresses a quality of the action itself or the subject’s state of readiness	Je suis prêt à partir.

This framework provides reliable guidance in most situations, though exceptions do exist.

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Part 1: Adjectives That Take “DE” — Subjective States

Adjectives that require de before an infinitive typically describe an internal, subjective experience of the subject. The subject is reacting emotionally or physically to the action being described.

Core List

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.
fatigué	tired	Je suis fatigué de travailler.
soulagé	relieved	Elle est soulagée de savoir.
ravi	delighted	Il est ravi de vous rencontrer.
désolé	sorry	Je suis désolé d’être en retard.
ennuyé	bored or annoyed	Je suis ennuyé de répéter.
horrifié	horrified	Il est horrifié de voir ça.
effrayé	frightened	Elle est effrayée de sortir.
inquiet	worried	Je suis inquiet de ne pas avoir de nouvelles.
lassé	weary	Je suis lassé de ces excuses.

Diagnostic Test

If the English equivalent can be rephrased as “I feel [adjective] that I do this,” the French construction will almost certainly use de.

• I am happy that I see you → Je suis content de te voir.
• I am tired that I work → Je suis fatigué de travailler.

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Part 2: Adjectives That Take “À” — Qualities and Readiness

Adjectives that require à before an infinitive describe either characteristics of the action itself or the subject’s state of preparedness or tendency. These are objective qualities rather than emotional responses.

Core List

Adjective	Meaning	Example
facile	easy	Ce problème est facile à résoudre.
difficile	difficult	Ce texte est difficile à comprendre.
prêt	ready	Je suis prêt à partir.
lent	slow	Il est lent à réagir.
rapide	fast	Elle est rapide à apprendre.
habitué	accustomed	Je suis habitué à travailler tôt.
enclin	inclined	Il est enclin à exagérer.
disposé	willing	Je suis disposé à vous aider.
habile	skilled	Il est habile à négocier.
prompt	prompt or quick	Elle est prompte à répondre.

Diagnostic Test

If the English equivalent can be rephrased as “It is [adjective] to do this,” where “it” refers to the action or object, the French construction will likely use à.

• It is easy to solve this problem → Ce problème est facile à résoudre.
• I am ready to go → Je suis prêt à partir.

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Part 3: The Exceptions — Words That Defy the Pattern

The 80/20 rule works well, but French has a significant number of exceptions. These adjectives do not follow the pattern described above and simply require memorization.

Exceptions That Take “DE”

These adjectives refer to necessity, importance, or certainty—categories that might suggest à but consistently require de.

Adjective	Meaning	Example
nécessaire	necessary	Il est nécessaire de partir tôt.
essentiel	essential	Il est essentiel de comprendre.
important	important	Il est important de vérifier.
urgent	urgent	Il est urgent d’agir.
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.

Exceptions That Take “À”

Adjective	Meaning	Example
déterminé	determined	Il est déterminé à réussir.

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Part 4: Adjectives That Change Meaning With Preposition

Several adjectives can take either à or de, but the meaning changes depending on which preposition is used. These cases require careful attention to context.

Adjective	With À	With DE
bon	Bon à manger = good to eat (describes the food)	Bon de savoir = good to know (describes the act)
mauvais	Mauvais à dire = bad to say (describes the thing said)	Mauvais de mentir = bad to lie (describes the act)
agréable	Agréable à regarder = pleasant to look at (object quality)	Agréable de vous voir = pleasant to see you (subjective feeling)
désagréable	Désagréable à porter = unpleasant to wear	Désagréable de vous déranger = unpleasant to disturb
utile	Utile à savoir = useful to know (for a specific person)	Utile de savoir = useful to know (in general)

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Part 5: Decision Framework

When uncertain which preposition to use, follow this structured approach:

1. Determine what the adjective describes:

• If it expresses a feeling or emotional reaction → use de
• If it describes a quality of the action or task → use à
• If it indicates readiness or tendency → use à

1. Check against the exception list:

• nécessaire, essentiel, important, urgent, obligé, sûr, certain, capable → use de
• déterminé → use à

1. For ambiguous cases, consult a dictionary or reference native examples.

This approach yields correct results in approximately 80% of cases. The remaining 20% are fixed expressions that require memorization.

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Part 6: Complete Reference Table

Category	Preposition	Adjectives
Emotions and subjective reactions	DE	content, triste, fier, surpris, fatigué, soulagé, ravi, désolé, ennuyé, horrifié, effrayé, inquiet, lassé
Task qualities and object characteristics	À	facile, difficile, agréable (with object), désagréable (with object)
Readiness, tendency, habit	À	prêt, enclin, disposé, habitué, lent, rapide, habile, prompt
Necessity and importance (exceptions)	DE	nécessaire, essentiel, important, urgent
Certainty (exceptions)	DE	sûr, certain
Obligation (exceptions)	DE	obligé
Determination (exception)	À	déterminé

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Part 7: Practice Exercises

Complete each sentence with à or de.

1. Je suis prêt _ partir.
2. Il est fatigué _ travailler.
3. C’est facile _ faire.
4. Elle est contente _ te voir.
5. Il est nécessaire _ vérifier.
6. Je suis déterminé _ réussir.
7. Ce livre est agréable _ lire.
8. C’est agréable _ te rencontrer.
9. Il est sûr _ gagner.
10. Tu es habitué _ conduire à gauche.

Answers: 1. à | 2. de | 3. à | 4. de | 5. de | 6. à | 7. à | 8. de | 9. de | 10. à

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Conclusion

The choice between à and de before an infinitive follows a consistent pattern in the majority of cases: subjective emotional responses take de, while objective qualities and states of readiness take à. However, approximately 20% of adjectives depart from this pattern and must be learned individually.

Practical recommendations:

1. Learn the 80% rule as a foundation: feelings → de; task qualities and readiness → à
2. Memorize the common exceptions
3. Consult reliable references when uncertain
4. Accept that occasional errors are normal in the learning process

While mastery of these prepositions takes time and exposure, understanding this framework provides a solid foundation for accurate usage. Native speakers will understand you even if you occasionally choose incorrectly, and consistent practice will gradually make these choices instinctive.