Si and sia: his own, or another man's

Si and sia point back at the subject of their own clause. English his can mean his own or another man's; Esperanto has a word for each.

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1. 1Ŝi staras kun sia hundo.
2. 2Ŝia aŭto atendas.
3. 3Ŝi tenas sian ombrelon.

Ŝi staras kun sia hundo: she is standing with her (own) dog. Ŝia aŭto atendas: her car is waiting; it is hers, but the car is the subject, so ŝia. Ŝi tenas sian ombrelon: she is holding her (own) umbrella.

The forms

Si is the pronoun, sia its possessive. Both take the ordinary endings: -n for the object, and sia agrees like any adjective.

• Li parolis pri si. - He talked about himself.
• Li defendis sin. - He defended himself.
• Ili venis kun siaj amikoj. - They came with their (own) friends.

There is nothing new in the endings: the -n is the accusative, and the agreement is the one from nouns and adjectives.

Third person only

Si serves the whole third person: he, she, it, they, and oni (one). I and you need nothing new:

There is only one mi in a sentence, so min is already clear. In the third person, lin could be a second man, so Esperanto spends a word on the difference.

Never the subject

Si points back at a subject, so it cannot be one, and sia cannot sit inside one. Use lia, ŝia or ilia there, even for the person's own things:

• Lia patro amas lin. - His father loves him. (never sia patro)
• Li kaj lia frato venis. - He and his brother came. (never sia frato)
• Lia hundo estas granda. - His dog is big. (never sia hundo)

In the second sentence, he and his brother are both the subject, so nothing in it can be sia.