The United States is famous in Europe for being prohibitive despite its status as a nation of freedom.  I have tried again and again to explain to my French and other European friends that one’s freedom in the United States ends when their acts fringe upon another’s freedom.  In any case, the French version of freedom is very liberal as compared to American standards.  So, let’s discuss a verb that can be used to explain in French the differences in these freedoms…in other words what ‘is necessary’ and what ‘must/mustn’t be done’.  This would be the verb falloir.

Here is how you conjugate this verb:

Il faut insister.  (You must insist.)
Il ne faut pas insister.  (You must not insist.)

Hmm…you are thinking, ‘where are the other conjugations???’  Well, falloir is an impersonal verb so it is only conjugated in the 3rd person singular.

So, here are some typical ‘must nots’ in the United States that my French friends ‘complain’ about:
Il ne faut pas fumer. (You must not smoke.)
Il ne faut pas faire du topless à la plage.  (You must not go topless on the beach.) 

And here is a typical ‘must’ in the United States:
Il faut avoir 21 ans pour pouvoir boire de l’alcool.  (You must be 21 to drink alcohol.) 

Conversely, here are some cultural ‘must nots’ in France:
Il ne faut pas parler à voix haute en public.  (You must not speak loudly in public.)
Il ne faut pas demander des questions personnelles.  (You must not ask personal questions.)

And some cultural ‘musts’ in France:
Il faut couper le fromage en parts égales.  (You must cut cheese in equal parts.)
Il faut donner le bonjour à tout le monde.  (You must say ‘good day’ to everyone.)

And finally, here are some more useful expressions with falloir.

Un homme comme il faut (the right kind of man)
Il fallait le dire (you should have said so!)
Il faut deux heures (it takes two hours)
Il leur a fallu quatre heures (it took them four hours)
Il te faut du repos (you need some rest)
Il ne faut pas se fier à cette fille (you must not trust this girl)
Il s’en faut de cent euros (there’s a shortage of a hundred euros)

Est-ce que vous pensez qu’il faut étudier la grammaire pour bien apprendre le français?