Learn French, Avoir:
You need to know TWO things to be able to agree correctly the past participle:
1. To answer the question: What? to know the Direct Object.
2. To answer the question: Where? to locate the Direct Object of the sentence (before of after the verb avoir).
J’ai mangé les pommes
1. Say What! What did I eat? answer: pommes (Direct Object)
As there is no preposition between the verb “mangé” and “les pommes”, we call “les pommes” the DIRECT object, as it comes directly after the verb.
2. Where is the direct object? before or after:
“Les pommes” come after the verb “avoir”
The rule is: When the direct object is after the verb “avoir”: no agreement!
So, we write “mangé” (no s at the end)
Nous avons écrit des lettres
Elle a envoyé une lettre
The rule is:
When the direct object is before the verb avoir, there is an agreement with this direct object.
Je les ai mangé (les = pommes)
1. Say What What did I eat? answer: les (Direct Object)
2. Where is the direct object? Before the verb Avoir, so there is an agreement.
“Les” is for “pommes” which is feminine plural.
Je les ai mangées is the correct sentence (so the first sentence above is not correct)
Nous les avons écrites (les = lettres)
Les lettres que nous avons écrites
Elle l’a envoyée (l’ = lettre)