SELECT categories user has not already selected

programming
1

I really have no idea how to approach this problem, or even what to search Google for.

There are a dozen or so categories that the user can choose from. The table structure is roughly like this:

TABLE Categories
categoryID - Primary Key
categoryName
caetgoryDescription

TABLE UserChoices
id - Primary Key
userID
categoryID - FK

Now, I want the user to be able to view a list of all categories that he has NOT yet chosen. Am I making myself clear? I have no idea even what way to think for that one…