He killed his father

“He killed his father!”

Did he kill his own father? Or did he kill another man’s father?

You and your feeble English just don’t know!

In Esperanto, there is a way of resolving this and similar kinds of ambiguity. The word for “he” is li. The word for “his” is lia. However, if we want to simply refer back to the subject of the verb (the one doing the action), we use the pronoun si (he/she/it) or or sia for possession (his/her/its). Therefore, if we don’t use some form of si we must be talking about someone other than the subject of the verb!

li mortigis lian patron
he killed his (someone else's) father

li mortigis sian patron
he killed his (own) father

(Remember the ‘n’ is just the accusative ending)

Simple yet useful!