Both are correct, but it depends on the situation. I believe that you would "use smth for smth" when the second "smth" is a noun, and "use smth to smth" when the second "smth" is a verb. For example: 1. I use my closet for storage. ("storage" is a noun) 2. I use my mouth to chew. ("to chew" is an infinitive verb) **Here is the tricky part: some verbs can function as nouns, depending on their placement in a sentence. They're called "gerunds". Let's use "cook" as an example. Both these sentences are correct: 1. I use my stove to cook. ("to cook" is an infinitive verb here) 2. I use my stove for cooking. ("cooking" is a gerund/noun here) (Dictionary entry for example: http://dictionary.reference.com/browse/cooking) Here are some links for further reading on this topic: http://www.englishpage.com/gerunds/noun_prep_gerund_list.htm http://learnenglish.britishcouncil.org/en/english-grammar/verbs/infinitive I hope that helps!

I think use pen to write is correct. It be better if you say ' pen is used for writing.'

Hello liel. I think too : use pen to write