Agreement of Past Participles in Compound Tenses

  I. Non-Pronominal Verbs
  A. Verbs whose auxiliary is avoir-- No agreement, unless Direct Object precedes the verb. And then, agreement with preceding Direct Object
  1. Elle a acheté une robe. (no agreement)
  2. Elle l'a achetée (la robe -- agreement with preceding Direct Object)
  B. Verbs whose auxiliary is être -- Always agreement with Subject.
  3. Elles sont descendues à neuf heures.
 
  II. Pronominal Verbs (Note: All pronominal verbs take être as auxiliary.)
    A. Verbs that are always, only pronominal (not many *) -- Agreement is made with Subject (i.e. the same rule of agreement as with non-pronominal verbs taking être as auxiliary).
  4. Elles se sont souvenues.
  * Some of the verbs that are always, only pronominal: se souvenir, se repentir, s'enfuir, s'abstenir, s'agenouiller, s'écrier, s'efforcer, s'évanouir, se révolter.
  B. Verbs that are pronominal, but that may be used also as non-pronominal verbs (the majority of pronominals) -- No agreement, unless Direct Object precedes the verb, and then, agreement with preceding Direct Object. This rule is the same, then, as with non-pronominal verbs taking avoir as auxiliary. Note: The preceding Direct Object will occur as a Reflexive Pronoun for pronominal verbs.
  5. Elles se sont lavées. (se is the preceding D.O.; agreement made with D.O.
  6. Elles se sont lavé les mains. (D.O. = les mains & D.O. does not precede verb -- No agreement. Se functions as an Indirect Object, indicating whose hands.
 
  7. Nous nous sommes arrêtés.
  8. Nous nous sommes parlé.
 
  Note that the verbs in the four examples (5.-8.) can be used non-pronominally, and then take avoir as auxiliary:
  For 5. and 6. : Elles ont lavé la voiture.
  For 7. : Il avait arrêté le voleur.
  For 8. : Tu auras parlé au président.

Summary: Rules at a Glance
Agreement
 
Non-Pronominals
Pronominals
  auxiliary: avoir auxiliary: être auxiliary: être
  None, except with preceding Direct Object Always with Subject 1. Verbs only pronominal -- agreement with Subject of verb
2. Verbs not always pronominal -- agreement only with preceding
Direct Object (in form of reflexive pronoun).