Agreement of Past Participles

Question

Hi,I am under the impression that when conjugating a verb in the passé composé, the past participle will agree in the following instances:When using avoir with a preceding direct object and using être and s'être. However, I have recently seen instances of conjugations of être/s'être not having any agreement.Could anyone please tell me why this is? For example, why is the following sentence correct?Les conférenciers s'étaient juré de nous renseigner sur l'histoire. Le genre s'était enrichi grâce à Ray Bradbury et à plusieurs auteurs qui se sont succédé tels que Stephen King et J.G Ballard. I would appreciate any responses,Thanks!Rebecca :)

Accepted Answer

Hi Rebecca,
The rules of agreement of past participles with reflexive verbs are complex so I will try to keep it simple.
In your second sentence it is particular to the verb se succéder which can never have a direct object  ( Petit Grevisse # 390) :
verbs like : se ressembler, se plaire, se suffire, se sourire etc.
e.g.
Les rois qui se sont succédé ...
Ils se sont plu l'un à l'autre.
In the case of your first example 
the direct object is 'de nous renseigner sur l'histoire' which is after the verb, se jurer de faire quelque chose, so the past participle doesn't agree.
Hope this helps!