Negative expressions
From the lesson on negative expressions I learnt that double negatives are used in spanish, but I am a little unclear about this.
For example Nunca necesitas papel. is fine
but my first thought was to say
No necesitas nunca papel.
Is this second form correct, the first is preferred just because it is shorter?
4 Answers
Good news Miguelito!! Both are correct!!
Well, just to mention the "rule"; if the negative word precedes the verb the double negative construction is not needed. When the negative word follows the verb the verb must be negated.
Nada es necesario.
No es necesario nada.
Is this second form correct, the first is preferred just because it is shorter?
I agree with Benz that both are correct. But it isn't just because it's shorter. Here is how I understand the difference:
Nunca necesitas papel.
You never need paper.
No necesitas nunca papel.
You don't ever need paper.
I think the double negative adds emphasis. That isn't true every time it is used, but that is the effect in this context. 
I am fairly sure (but not totally positive) that they are both correct.
However, your assumption that "shorter is better" is correct, insofar as standardized testing is concerned. In normal conversation however, either would be fine.
