A method for classifying the function of a source in supporting an argument made in a piece of writing. Understanding the source's function can help you determine if a source is reliable in a particular context. For example, when faculty say that only scholarly or peer-reviewed are acceptable for an assignment, they often mean that your argument and method sources must be scholarly, but do not expect that your exhibit sources (e.g. a poem, a historical document, government produced data, the results of an original experiment) will be peer reviewed.