On vs nous
Both of them mean "we", but why "on" is known as a third person?What's the difference between them?
In some poems "on" is mentioned as people in general like :
Quand on a tout, on est trop plein. -Joseph Joubert
When you have everything, you are too full (satisfied).
On a souvent besoin d'un coup de main --rarement d'un coup de pied. -Louis-Auguste Commerson
People often need a hand, rarely a kick.
That's pretty much it. "On" can be used for something vague like "you/one" or in place of the passive voice, when you want to say that something happened but not focus on who did it. "On sonne" = the doorbell rang - there is someone at the door - someone rang the bell but we don't know who.
A discussion on Quora - https://www.quora.com/Why-do-the-French-use-on-instead-of-je-nous-etc - discusses its usage.
Today I encountered this approximate sentence: We have to be elegant to go to this restaurant.
I submitted: On doit être élégant... But Duolingo insisted on: On doit être élégants...
The hints didn't offer élégant, which I thought was strange. When I looked at the discussion (on my phone), one person said that "élégants" was correct because the English sentence used We (plural pronoun). Is that true?
I reason that On is 3rd person singular so the agreeing adjective must also be singular. I would like a ruling on this, please.