Learn Swedish: Kvinnan ställer sin gräsklippare på hans uppfart. - The woman puts her lawnmower on his driveway.

In Swedish, when a "third person" subject (he, she, it, or they) owns the object being talked about, we must use the reflexive possessive sin (or sitt/sina). Because the woman is the subject of the sentence and she is moving her own lawnmower, we use sin. If we used hennes, it would mean she is putting some other woman's lawnmower on the driveway!

Why do we use hans uppfart at the end of the sentence instead of sin uppfart?

The word sin always points back to the subject of the sentence (the woman). The driveway belongs to a man ("his driveway"), so it doesn't belong to the subject. Because of this strict rule, we cannot use sin here; we must use the regular possessive word hans.

Why is the form sin used here, rather than sitt or sina?

The form of the reflexive possessive must match the gender and number of the noun it describes. Since gräsklippare is a singular en-word, we use sin. If she were parking a vehicle (an ett-word, like ett fordon), it would be sitt fordon, and if there were multiple mowers, it would be sina gräsklippare.

Why does the Swedish sentence use ställer for "puts"? Could I use ?