надо и нужно

[ddvossler]

надо means I must, I should, I need to - with a moral like obligation implied:
"I need to call my mom." (guilt guilt guilt)
"I should give to charity." (guilt guilt guilt)
(должен is a ought to/should/must also with a hint of moral obligation but is used with nominative nouns - unlike надо and нужно which are used with dative nouns)

нухно is a more straight forward need without moral obligation implied:
"I need a pencil for this task."
"I should buy a cell phone for this job."

[watsong]

I think that I understand. Thank you.

Мне надо такси (A taxi is necessary to me in order to get where I am going.)
Мне нужно такси (I need a taxi but could also take an alternative, like a bus.)

[baggieonline]

I think there is a big difference in the negatives. Unless I am mistaken:

ne nado + infinitive = shouldn't do something.
ne nuzhno + infinitive = it's not necessary to do something

Apologies for not writing in Russian - posting this from my PSP.

[roxanasharie]

As a native speaker I can say that there`s no real difference in надо and нужно. Although you won`t find надо much in written Russian, because it`s a very colloquial form of "I need" and not used even in polite conversations. The usage of these words is also a little different. Usually we don`t put nouns after "надо" as in the examples above: "мне надо такси". It sounds much more correct if you use it with the verbs: "Мне надо идти"-I have to go. "Нужно" is also used exclusively with verbs, but you can use it with nouns IF you modify this word according to genders:

Мне нужен телефон - I need a phone
Мне нужна ручка - I need a pen
Мне нужны деньги - I need money

You probably came across "надо" a lot more often on RussianPod. But that`s just for the total beginner lessons, because "надо" is not modified according to genders and is easier to pronounce. Although... personally I wouldn`t recommend using too much, it`s rather slangy. Like "I gotta go" maybe, though it`s hard for me to catch the feeling of the English "gotta" "havta"

Должен - is a totally different story. It just mean "must, have to" and implies obligation.
And again, "надо" and "нужно" have the same meaning - "need, should", and only differ in usage and level of speech.

[watsong]

I am very pleased to hear the real usage of these words.

This thread demonstrates, that it is important to know whether someone is a native Russian speaker before fully believing their statements on Russian language.

Thus, for me, 'roxanasharie' is now an authoritative figure on Russian language learning.

Thank you very much, roxanasharie!