Usar vs servir
Why is the verb servir used in these expressions instead of usar: Tengo aquí una pluma que sirve para escribir. Las tijeras que sirven para cortar papel.
5 Answers
It´s mostly a style thing. If you´ll note, the verb ´to use´ often takes the passive voice.
Scissors are used to cut paper.
But servir (to serve to) takes the active voice, which some writers and some types of communication prefer .
Las tijeras que sirven para cortar papel.
The scissors serve to cut paper.
That particular construction is a tick odd in English, but with other words, it sounds quite normal. A modem serves to connect a computer to the internet.
So, it seems mostly stylistic.
Now, I have my own question. What purpose does the que serve here? (why is que used here) ?
Las tijeras que sirven para cortar papel.
If I had had to translate into that sentence, I would surely have left out the que.
To Mikeca: The words Sirve and Sirven can mean to serve or to work with the word in the sentence as if you are saying "Here I have a pen that works to write" as in to serve its purpose. The pen does not work, to a spanish person it means labor or job, but really in the sentence its used as the pen's purpose, it does not work. Sirve and Sirven works the same way. I hope this helps. I always add a little extra information so everyone can understand it better. Good luck, I hope this helps. 
In addition, the difference between the two words is the nuance of who/what does the action.
"Las tijeras no sirven (para nada)" ..... "the sissors don´t work / they are broken". If we say "las tijeras ya no se usan", we are saying "the sissors are no longer used" but they are probably still functional.
In these cases, "servir" is normally used when emphasising the thing being used and "usar" emphasizes the user of the thing.
To Rogspax: Las tijeras que sirven para cortal paper = The scissors that work for cutting paper. The "QUE" could have been left out and this is what you get = The scissors work for cutting paper. So the que stands for that. That pencil is red, The pencil that bends, these are different sentences that make the word "that" mean different. Same this with "que" I hope this helped,
@JulianChivi
When you say "Las tijeras no sirven." could you also say "Las tijeras no funcionan"? How about "Las tijeras no andan"?
Just a few questions I have about this too.
