188.8.131.52.2 agreement in gender and number with the past participle
You very often found the correct statement that a past participle must agree in gender and number with the direct object if this stands before the verb.
L' ho visto. => I saw HIM.
L' ho vista. => I saw HER.
Li ho visti. => I saw THEM (plural, masculine)
Le ho viste. => I saw THEM (plural, feminine)
At the other side you find the equally true statement that only in the case that the direct object is lo, la, li, le the present participle must agree. These are two different statements. The first statement says that the past participle must agree with every direct object, the second statement means that it must agree only with lo, la, li, le.
Let' s see an example.
only lo, la, li, le agrees
A miei amici li ho visti.
A voi vi ho visto.<=== (normal)
every direct object agrees
A miei amici li ho visti.
A voi vi ho visti.<=== (controversial)
There is a controversial debate about that point in Italy. For those who speak French. In French it is very clear, every direct object in front of the verb matches with direct object. The statement below is from a well-known Italian linguist. He said that the agreement is only necessary in case of lo, la, li, le and he says that this corresponds as well to the normal use in nowadays Italian.
"Non basta dire che la concordanza del participio è obbligatoria solo nel caso di un pronome personale: occorre assolutamente precisare che tale obbligo sussiste solo quando il pronome è di terza persona ("lo", "la", "li", "le"). Negli altri casi ("mi", "ti", "ci", "vi", a cui si può aggiungere il "ne" partitivo) la concordanza è infatti facoltativa, e non rappresenta neppure la soluzione più comune: una ragazza, ad esempio, riferendosi a sé e alle compagne, otto volte su dieci dirà "spero che non ci abbia visto" anziché "spero che non ci abbia viste"."
"It is not enough to say that the agreement of the past participle is compulsory in case that there is a personal pronoun. It is necessary to specify that this is only compulsory in case that the personal pronoun is in the third person ("lo", "la", "li", "le"). In all the other cases ("mi", "ti", "ci", "vi" and the partitive article
"ne") this agreement is optional and not at all the most common version. A girl for instance talking about herself and her friends 8 times out of ten would say 'spero che non ci abbia visto / I hope he didn't see us instead of 'spero che non ci abbia viste / I hoped he didn't see us."
At the other side there are people in Italy who ask why mi, ti, ci, vi should be handled in another way than lo, la, li, le. There are people who say that it has to be done as in France, one should say:
Ti ho vista (I saw you / in case that it is a woman)
Some Italians ask why there must be agreement in case of lo, la, li, le
Li ho visti
but not with mi, vi, ci
Vi ho visto / visti
They say that it is necessary to be as consequent as in French. The solution for us is quite simple. The best thing we can do is to make it as the mayority of the Italians. After lo, la, li, le there must be an agreement, and after mi, ti, vi, ci the agreement is optional. You can do it, but is not compulsory.