The predicative is a part of a sentence which is neither subject, nor object, nor verb, nor preposition term. Yet it relates to the verb somehow. I am not sure if the predicative is exactly the same as indirect object. Some examples are
Ili estas lacaj
Ĝi farbas la domon ruĝa
However, it can also be more complicated (examples taken from tekstaro)
Oni petis lin solvi la disputon
Ĉi tiuj konoj igis ilin observi la astrojn
Are there some rules for which verbs can use the predicative? Is there some default meaning of the predicative?