What is the element which serves as a main idea in an artist’s composition? Is it the subject matter?

Answer 1

http://www.google.com/search?q=main+idea+in+painting&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

If you look through these various results, you'll find that you're correct.

=)