Interdire vs. proscrire vs. défendre
The French words interdire, proscrire, and défendre all convey the idea of forbidding or prohibiting something, but they differ in their intensity, register of language, and typical usage contexts.
Interdire
The verb interdire is the most common, neutral, and versatile word for expressing prohibition in French. It is used in everyday conversation, formal rules, and legal contexts to state that an action, behavior, or item is not allowed.
Le médecin lui a interdit de manger trop de sucre.
(The doctor forbade him from eating too much sugar.)
Il est strictement interdit de stationner devant cette porte.
(It is strictly forbidden to park in front of this door.)
La nouvelle loi va interdire l'utilisation de ces produits chimiques.
(The new law will prohibit the use of these chemicals.)
Je t'interdis de me parler sur ce ton.
(I forbid you to speak to me in that tone.)
L'accès au chantier est interdit au public pour des raisons de sécurité.
(Access to the construction site is prohibited to the public for safety reasons.)
Proscrire
The verb proscrire is a strong and formal word meaning to ban, outlaw, or completely eliminate. It is typically used when a practice, substance, or behavior is rejected because it is considered harmful, dangerous, or obsolete.
Ce régime alimentaire strict proscrit totalement les aliments frits.
(This strict diet completely bans fried foods.)
L'usage des téléphones portables est à proscrire pendant les réunions importantes.
(The use of mobile phones is to be banished during important meetings.)
Le gouvernement souhaite proscrire les emballages en plastique à usage unique.
(The government wishes to outlaw single-use plastic packaging.)
Il faut proscrire cette expression de notre vocabulaire car elle est très offensante.
(We must banish this expression from our vocabulary because it is very offensive.)
Cette méthode de travail est désormais proscrite par la direction.
(This working method is from now on prohibited by management.)
Défendre
While défendre frequently means to defend or protect, it is also widely used to mean to forbid. When used for prohibition, it carries a slightly more authoritative, traditional, or protective tone, and is very often found in official warning signs or parental commands.
Ma mère m'a défendu de sortir tard le soir.
(My mother forbade me from going out late at night.)
Il est défendu de fumer à l'intérieur de cet établissement.
(It is forbidden to smoke inside this establishment.)
Le règlement de l'école défend aux élèves de courir dans les couloirs.
(The school rules forbid students from running in the hallways.)
Son avocat lui a défendu de répondre aux questions des journalistes.
(His lawyer forbade him from answering the journalists' questions.)
La religion leur défend de consommer ce type de viande.
(Their religion forbids them from consuming this type of meat.)
Summary
To summarize, use interdire as your standard, everyday word for general rules and prohibitions. Choose proscrire when you want to sound formal and emphasize a strong ban on something harmful or unwanted. Opt for défendre when dealing with authoritative commands, protective parental rules, or traditional warning signs.