French language Q&A Forum

I have seen the phrase avoir à a couple times, and I was wondering how it differs from il faut and devoir - is it a less formal version of both of them, a more informal iteration of only one, or is it a completely different idea that it expresses

I have seen both of these being used, but I'm wondering if there is a semantic/pragmatic difference between the two e.g:

Il me faut partir

Il faut que je partisse.

Do these two convey a different idea, do they express different levels of formality, or are they completely interchangeable the only difference being that the former option takes less time to say

Can i say ‘vous allez devoir trouver’ ?

Why can’t i say ‘tout à fait!’ For ‘absolutely’ ?

I understand the lesson as it is taught above. 

In the lesson for future antérieur (Conjugate vouloir/pouvoir/devoir in the future perfect in French (Le Futur Antérieur)) there are sentences like "Nous aurons voulu le revoir". Why not Nous le aurons voulu revoir?

Is there another rule applicable when using future antérieur?

Isn't the causative always to or for the subject of the verb?

Why is this incorrect?  Il est aussi riche qu'ils