> If you see me dancing up and down, you might conclude that

> puch vIlo'nIS I need to use the toilet. Going to the bathroom will

> result in the benefit of not peeing in my pants, but no one is

> requiring me to go. If you're my boss and you tell me puch yIlo'

> use the toilet! I can now truthfully say puch vIlo' net poQ I am

> required to use the bathroom, because you are the outside

> agency making the demand, and it's my job to do what you say,

> regardless of the state of or danger to my pants. I can also

> continue to say puch vIlo'nIS, because my own personal need

> has not disappeared, but it says nothing about your demand.

I still don't get it.  What's the difference between the agency of the boss and the agency of the bladder?

Wait, there's one last element: need implies a kind of personal urgency; must or have to has less of such a sense; any urgency is imposed from outside.

Really, there's a ton about this easily found: http://lmgtfy.com/?q=difference+between+need+and+must

-- 
SuStel
http://trimboli.name