So, this happens a lot:

• A teacher assigns a paper in very vague terms
• And then when students ask for clarification, they refuse to give it
• And think of this as providing students with freedom
• But actually have something in mind and are upset when students don’t do it

For instance:

• Student: How long should the paper be?
• Teacher: As long as it needs to be.
• This isn’t a helpful answer, because length is an important parameter.
• A better answer would be something like “On the order of 3-5 pages, but it’s ok if it’s a bit longer or shorter”.

Or: 

• Student: What should I write about?
• Teacher: Something that interests you about the topic
• This is an unhelpful answer because a student who says something like that is asking for help. 
• You probably have a range in mind of what is and is not on topic, and it might not be as obvious to your students as it is to you
• A better answer would be: It’s a fairly open assignment. I’m always surprised by the ideas students come up with that I hadn’t thought of, so I don’t like to be too prescriptive about topics. Would you like help figuring out a topic that will work for you?

Or:

• Teacher (in response to students asking for clarification): There are no right or wrong answers
• This is unhelpful, because there probably *is* a range of what you will consider correct.
• Even if it doesn’t involve taking a particular position, there are attributes a correct answer will have, and it’s helpful to be explicit about them
• If you’ve not given this kind of exam before, it might be hard for you to know in advance what a correct answer will look like
• But it’s something you should be paying attention to as you get more experience at grading
• If you want students to explicitly reference assigned material, say so. If you want them to bring in more outside material, say so. If you want them to consider specific positions, say say.
• This may be obvious to you, but it’s not obvious to all of your students (including students who are entirely capable of doing the assignment the way you want if you tell them what it is)

Short version: When students ask for clarification of an assignment, help them to understand what it is you’re assigning. Scroll up for some specific examples.