4. When it is derived from an intransitive verb, the Participle Past is always invariable.

Ils or elles se sont plu,
Ils or elles se sont nui,
They have pleased each other.
They have injured each other.

5. When joined to the verb avoir, it never agrees with its nominative.

ma fille m'a écrit, my daughter has written me.
les enfants ont pleuré, the children have wept.

6. But it agrees with its direct object (see sec. 3) when preceded by it.

Les fleurs qu'elle m'a données,
Les lettres que j'ai écrites,
Les dames qu'il a connues,
The flowers which she has given me.
The letters which I have written.
The ladies whom he has known.

7. Placed after it, it remains invariable.

J'ai écrit les lettres,
Il a connu les dames,
I have written the letters.
He has known the ladies.

§ 51. The Adverb.