"They present their idea."
Translation:De presenterar sin idé.
Varför inte också "de presenterar idéen"? Jag tänkte att man skulle anta att idéen var deras.
Yes, but we also have the pattern "Hon tvättar sig händerna", meaning her hands and not merely the hands; hence my question.
It's either Hon tvättar händerna or Hon tvättar sig om händerna, but you're right that we often use the definite when English would use a possessive. (I always link to this discussion so I'm adding a link there here too: https://www.duolingo.com/comment/6014446 for any users who haven't seen it already)
I think it's not that obvious that an idea is your own – the perfect example is body parts, where you really are most likely to speak about your own ones, like Jag borstar tänderna = I brush my teeth, it's less likely that you would brush anybody else's teeth. If somebody said De presenterar idén, I would not assume that it was their own idea.