I don't know. As furrykef said, there are strange coincidences betweeen Spanish and English, but they are probably only that ,coincidences . About this kind of sentences, there are two options in Spanish:
- To use "uno" ( pronoun) as the subject : Uno debe hacer esto, uno debe ser así...
-To use the reflexive pronoun "se", which is used in Spanish in many situations: Se debe hacer esto, se ha de ser ser así... Note that here "se" is not the subject, it simply does not exist. On in French is like "se" in Spanish, isn't?
Maybe English later adopter on from Norman French and thus in English it's "one must be polite".
Guest : « Another interesting construction seems to be the French "on a a etre poli" which corresponds exactly to "one has to be polite" and "man hat höflich zu sein". »
Sauf que le français utilisera cette construction : Fr <on doit être poli> ~ Al <man muß höflich sein>.
Voyons les occurrences dans gougueule :
<man hat höflich zu sein> → 1
<man muß höflich sein> → 75
*<on a à être poli> → 0
<on doit être poli> → 1.270
L'expression An <au courant with> (empruntée au français) donne 18.300 occurences → <I'm au courant with the intricacies of social networking>.
Herbist : « It French, the relatively original construction "tiens mois au courant", meaning "keep me informed", is a litteral translation of the German "halte mich auf dem Laufenden" and English "keep me current".
While the English saying may be a borrowing of the French, it is unclear to me whether the Germans borrowed als the construction from French or vice versa? ».
D'après le TILF, l'expression <au courant> était utilisée pour <au courant des affaires> à l'origine (attestée dès 1690). D'après cette même source, le tour <au courant de qqch> est daté de 1780.
C'est tiens MOI au courant. In French mois means month not me