Use of нужно with the dative?

Question

What affects how the ending of нужно should be changed? A corrected sentence I wrote reads >Ксения говорила, Мне нужно его общество как собаке нужны блохи. Why are нужно and нужны used? (And I realize now that Russians say как собаке пятая нога which is not exactly something said in English, but it's clever!)Does надо also change similarly depending on what noun is associated with it?

Answer 1

I need + object (something)

I need money.

Мне нужен телефон. m

Мне нужна машина. f

Мне нужно молоко. n мне нужно общество

Мне нужны деньги. pl собаке нужны блохи

Answer 2

When this word is used with an infinitive, it is always нужно, as in "Мне нужно пойти домой." Note that one of the satisfying things about Russian grammar--there are many--is that one can say "always."

However, when this word is used with a noun or noun phrase without an infinitive, it is simply a short adjective, and therefore ti takes the endings that other common short adjectives take, such as уверен and доволен.

What may be confusing you in the (clever) sentence above is that the word is used as a short adjective with the noun общество, whose ending marks it as a neuter. Therefore the word is нужно, which happens to coincide in spelling with the word used with infinitives. Remember--the thing to ask yourself is whether the word is used with an infinitive.