Rule #1
The first rule for agreement of past participles is as follows:

When the auxiliary ("helping") verb used to form compound tenses (passé composé for example) is être, the past participle must agree in number and gender with the subject of the verb (very much like an adjective).

Examples:
Les filles sont arrivées à huit heures.
Mes amis sont partis de bonne heure.
Ma sœur est tombée.
Ils sont rentrés.

Rule #2
The second rule concerns verbs that use avoir for the helping verb to form compound tenses. These constructions may have a direct object. When the direct object is placed after the past participle, no agreement is necessary.

Example:
Ma famille a acheté une nouvelle maison.

There is no agreement here because the direct object (maison) follows the past participle. However, when the direct object comes before the past participle, we must have agreement between the direct object and the past participle.

Example:
La maison que ma famille a achetée est blanche.

In this case, maison is the direct object of the verb and agreement is necessary. (Maison is the direct object of the verb. Agreement is necessary because, by the time we get to the verb, we know what had the action performed on it. The past participle then acts like an adjective and must agree in number and gender with the object it acted on.)

Object Pronouns

In French, object pronouns are placed before the verb (except in the case of affirmative commands). For this reason it is necessary to watch for agreement between a past participle and a preceding direct object, which may be a noun or a pronoun. There will never be agreement with indirect objects.

Quite often a past participle is used in the same way as an adjective—to describe. The common expression déjà vu is an example. It expresses the idea that something has already been seen (vu) by using the past participle. If a noun is used, agreement is necessary.

Some more examples:

• des messages écrits
• les leçons bien préparées
• les papiers retrouvés
• une photo prise
• des œufs vendus
• les livres déjà lus

Se Verbs

You will need to be very careful of past participle agreement when dealing with se verbs. Remember:

However, if a more specific direct object is added, the se becomes an indirect object.

Example:
La fille s'est lavé les mains.

Now the direct object is les mains and the indirect object is la fille. (She, of herself, indirect, washed the hands, direct.) You will need to be very attentive to the exact meaning of the verb; for example, se parler may mean either (1) to talk to oneself (2) to talk to one another. The common use is to talk to one another. There will be no participle agreement since there is no direct object possible.