sarebbe piaciuta la festa

would have liked the party

→ essere
phrase Uncommon #19,946
would have liked the party With piacere, the thing liked is the grammatical subject, so la festa causes piaciuta to agree in the feminine singular. The person who likes it is expressed with an indirect-object pronoun or phrase, such as a voi (to you).
IT: A loro sarebbe piaciuta la festa.
EN: They would have liked the party.

Pensavo che a Tom sarebbe piaciuta la festa.

I thought Tom would enjoy the party.

Sapevo che ti sarebbe piaciuta la festa.

I knew you would like the party.

A voi sarebbe piaciuta la festa di Tom.

You would have liked Tom’s party.

Sapevo che a Tom sarebbe piaciuta la festa.

I knew Tom would enjoy the party.

Pensavo le sarebbe piaciuta la festa.

I thought she would like the party.

Non pensavo che ti sarebbe piaciuta la festa.

I didn't think you would enjoy the party.

Sapevo che non ti sarebbe piaciuta la festa.

I knew you wouldn’t like the party.

Le sarebbe piaciuta la festa di Tom.

She would have liked Tom's party.