Pronominal form agreement
The past participle of pronominal verbs follows a different rule of agreement than the auxiliary "être" even if the pronominal form is formed with "être". Globally and before going into detail, the agreement must be done as if it were the auxiliary "avoir".
Agreement with the subject
Passive or neutral pronouns with no object complement COD or COI agree with the subject.
Verbs that are essentially pronominal, i.e. that only conjugate in the pronominal form (eg: s'enfuir) are conjugated with the subject.
- nous nous sommes méfiés. (verb essentially pronominal)
- la guitare s'est vendue facilement. (verb with passive sense)
- ils se sont aperçus du problème. (verb with neutral sense)
Verbs of reflexive and reciprocal meaning
The past participle is granted with the direct object complement (COD) if it is placed before the verb (as for verbs conjugated with "avoir"). The COD can be the reflexive pronoun or another word in the sentence. In general, a COD can be recognized by asking the question what? These verbs are said to be transitive.
If the following is an indirect object supplement (IOC), as with "avoir", there is no agreement. IOCs are introduced by prepositions such as "à", "de", "par" and so on. These verbs are called intransitive.
- ils se sont habillés.
===> reflexive verb
- nous nous sommes rencontrés.
===> reciprocal verb
- voici les vêtements qu'il s'est achetés.
===> agreement with vêtements, COD in front of the verb
- ils se sont acheté des vêtements.
===> COD after the verb: no agreement
- ils se sont plu.
===> intransitive verb, no agreement
- les secondes se sont succédé.
===> intransitive verb, no agreement
Pronominal verbs followed by an infinitive
The past participle is granted with the COD placed before the verb if the COD does the action expressed by the infinitive (as with the auxiliary "avoir").
- Nous nous sommes entendus chanter à la radio.
===> infinitive: to sing action is done by the COD (nous) so agreement
- Nous nous sommes vu féliciter par le moniteur.
===> infinitive: action is done on voir, no agreement