There are two basic ways to think about the role of supporting materials. Either they 1. clarify, explain, or provide specifics (and therefore understanding) for the audience, or 2. prove and back up...

There are two basic ways to think about the role of supporting materials. Either they

1. clarify, explain, or provide specifics (and therefore understanding) for the audience, or

2. prove and back up arguments and therefore persuade the audience. Of course, some can do both.