Causative faire (faire + infinitive)
Summary
Faire + infinitive means to have or make something done by someone else; the two verbs form a block that pronouns and most adverbs cannot split, and the participle fait stays invariable before an infinitive.
Explanation
The causative construction with faire expresses that the subject does not perform an action itself but has it performed, or makes someone perform it. Faire is conjugated and is immediately followed by an infinitive: je fais réparer ma voiture ('I have my car repaired'), elle fait pleurer les enfants ('she makes the children cry'), le professeur fait travailler ses élèves ('the teacher makes his pupils work').
Faire and the infinitive behave as a single unit, and nothing normally comes between them: you do not place the object in the middle. So 'je fais ma voiture réparer' is wrong; the noun object follows the whole block: je fais réparer ma voiture. Any object pronoun is placed before faire, not before the infinitive: je la fais réparer ('I have it repaired'), il les fait travailler ('he makes them work').
When two participants appear — the person caused to act and the thing acted on — French marks the causee. With a single object after the block, that object is direct: je fais travailler les élèves. When the thing acted on is already present as a direct object, the person made to do it is introduced by à or par: je fais réparer ma voiture à / par le garagiste ('I have the mechanic repair my car'). Par tends to name the actual doer, à can feel more like an indirect object.
A firm spelling rule: the past participle fait is invariable when it is immediately followed by an infinitive, regardless of any preceding direct object. So la voiture que j'ai fait réparer (not 'faite'), and les robes qu'elle a fait faire (not 'faites'). This overrides the normal avoir agreement rule and is a frequent point of error.
Closely related is se faire + infinitive, which gives a passive-like or 'arrange/suffer' meaning where the subject is affected: il s'est fait voler son portefeuille ('he got his wallet stolen'), elle s'est fait couper les cheveux ('she had her hair cut'). Here too fait stays invariable before the infinitive (s'est fait, never 'faite'), even with a feminine subject.
Rule of thumb: keep faire and the infinitive together as a block, put object pronouns in front of faire, introduce the human doer with à or par when there is already a direct object, and never make fait agree when an infinitive follows it.
Examples
Je fais réparer ma voiture au garage. — I'm having my car repaired at the garage. (Causative: the subject has the action done, not done by themselves.)
Ce film triste fait pleurer tout le monde. — This sad film makes everyone cry. ('Make someone do': faire pleurer; the object follows the block.)
Mes clés ? Je les ai fait copier hier. — My keys? I had them copied yesterday. (Pronoun les before faire; fait invariable before the infinitive copier.)
Le directeur fait travailler son équipe le week-end. — The manager makes his team work on weekends. (Single object after the block is direct: son équipe.)
Elle s'est fait couper les cheveux ce matin. — She had her hair cut this morning. (se faire + infinitive; fait stays invariable even with a feminine subject.)
La maison qu'ils ont fait construire est immense. — The house they had built is huge. (fait, not 'faite', because an infinitive (construire) follows it.)
Common mistakes
Elle s'est faite couper les cheveux.
Elle s'est fait couper les cheveux.
In the causative construction se faire + infinitive, the past participle fait is always invariable when followed directly by an infinitive, regardless of the subject's gender. Because couper follows fait here, fait cannot agree with the feminine subject elle: it must stay fait, not faite.
Related rules
causativefaireinfinitiveparticiple-agreement