help- structure of a sentence: 'L'on"

[Peter En]

I am familiar with indirect and direct object pronouns placing the le, la and les etc before the verb(or auxilary verb etc)

but I sometimes come across this:

"l'on", with on being the subject.

 

e.g.

on apprend ce que l'on doit apprendre

 

can someone please explain to me why le precedes on?

 

[George Hunt]

I think the  reason you add the l apostophe (in si l'on ) is to separate the two vowels (the i at the end of si and the o at the beginning of on  ,for example)  which makes it sound nicer.

However this "rule" applies mainly to written French  and "si on"  ,"qu'on "  etc is common enough in spoken French I think.

[Neil Coffey]

Yes. This has come up before on the forum: it's essentially a euphonic device (that's a fancy of way of saying "people use it when they think it sounds nicer") used in formal writing.

There are a few corner cases where it generally isn't used or where different authors disagree about when exactly to use it.