Hello, I suppose I should be getting used to this as I asked about Est-ce que a while ago.  So, I've been all content using J'ai besoin de for I need but now am finding Il me faut for I need, but also see Je dois me for I need.

So, why are there 3 versions of I need?  Is one to be used more than the other, formal or different circumstances? Am I safe to just use J'ai besoin de?

Any help is much appreciated!

Thank you.

The three forms are based more on what kind of "need" you are trying to convey. Le besoin is the noun for "(the) need" so it's used more for constructing sentences where you need a thing or object.

Ex: J'ai besoin d'aide - I need help. [Literal: I have need of help.]

Devoir is the verb for "to have to", so it's used more in the context of "needing" to do something, particularly, dual verb constructions.

Ex: Je dois aller chez le médecin. - I have to go to the doctor / I "need" to go to the doctor. [Note: it doesn't use a reflexive pronoun all the time, unless you are using a pronominal verb or some similar construction]. The tone is direct.

Falloir is an impersonal verb for "to be necessary", so it's used in passive constructions to show a "general" need (i.e. you're not "tasking" anyone in particular to provide you with something). The tone is more indirect.

Ex: Il me faut du temps pour apprendre la leçon.
Literal: It is necessary for me time to learn the lesson.
Gist: It takes me a while to learn the lesson. (i.e, I "need" some time to learn it.)

As an aside, the French also use the expression "Il faut que je te laisse" when ending a call, which is equivalent to "I have to hang up now" (also impersonal). In this case, the impersonal construction sounds more tempered or "gentle" -- like in the English equivalent --  than saying "I am hanging up on you" or "I'm leaving you", which sounds more pointed and personal.

Salut,

Your explanation is perfect Torusan. I think another good way of looking at this issue in whether or not the need is internal or external. For example:
*J'ai besoin d'aller faire du shopping. "I need to go do some shopping."
     Here we can see that your need to go shopping is not motivated by any external pressure but rather comes from self motivation to do so. Of course, you may have various reasons to go do that shopping, some of which may be cause by external influences but the motivation to complete the task still comes from you yourself.
*Il me faudra faire du shopping avant d'y aller. "I'll need to do some shopping before going."
     Here we can see that the motivation does not come from an internal need or desire but rather there is an external pressure caused by the need to have bought something before going somewhere.

This is how I like to think of the difference between the two.

I hope this helps and keep up the good work!

   -   Marie-Claire