“He killed his father!”
Did he kill his own father? Or did he kill another man’s father? You 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, we use the pronoun “si” or in this case, “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!
1. Li mortigis lian patron.
2. Li mortigis sian patron.
(Remember the ‘n’ is just the accusative ending)
Sentence 1 means “He killed his (someone else’s) father”. Sentence 2 means “He killed his (own) father”.
Simple yet useful!