The indirect object

mi, ti, gli/le, ci, vi, gli. The first four look like the direct ones; only in the third person do the two sets part company. gli is to him, le is to her. In spoken Italian gli also does duty for to them, where writing puts loro after the verb.

Which set applies is decided by the verb, and this is where English is not merely unhelpful but actively misleading. English marks the indirect object with to, or with word order — I write to her, I write her — but a great many English verbs simply take a direct object where the Italian one takes a.

telefonare a qualcuno is the clearest case: to telephone somebody is direct in English and indirect in Italian, so it is gli telefono and le telefono. The same goes for chiedere a (to ask somebody), rispondere a (to answer somebody), credere a (to believe somebody) and piacere a.

There is no way to derive this from English. The verb has to be learnt with its preposition, exactly as an English learner learns to look at, to listen to, to wait for.

One consequence worth keeping: after an indirect pronoun the participle does *not* agree. Le ho scritto, not scritta — which is the quickest way to check which set you have used.