[dragonsky]

Why not just ask "what problem are you trying to solve?", or "What do you want it to do?"?.. Not only does this put the requirement back on the asker to describe what they want you to do, it removes your preconceptions from the request.

A mistake I often see myself making is that as soon as I get asked to do something I stop listening and start planning how I'm going to implement the solution. In many cases my preconceived solution will not solve the actual problem, because I've not actually found what the problem is that needs to be solved.

In many cases the requester doesn't really know what they are asking for and will need some prompting to actually think it through. This requires a discussion, rather than a simplistic request to define "use case".