Theme and Controlling Idea

Most people would agree that theme and controlling idea are quite similar concepts. The main difference, I would suggest, is that theme is often specifically tied to the way we respond to a work of literature, while controlling idea offers a more general way of thinking about responding to a wide range of writing, including non-fiction work.

Theme is often described as what a literary work tells us, though never directly, about life, about the problems we face as human beings, about the issues we struggle with. Theme is usually the issue the work of literature addresses plus what the story tells us about that issue.

Same thing with controlling idea, except it can tell us about a broader range of issues. For example, a controlling idea could be found in a scientific paper. The controlling idea is usually the topic addressed in the work plus what the work says about that topic.

Try looking here for what I think is a pretty good descpription of the difference between a topic or issue and what the work says about the topic or issue.