Once you've identified the arguments for and against something, you'll be able to search for sources directly on those arguments. To locate for/against, search on your topic in one of our argument/debate databases, such as:
Opposing Viewpoints (Gale In Context)
Issues and Controversies
CQ Researcher
ProCon.org
ProCon.org, a free website, strives to "present controversial issues in a straightforward, nonpartisan, and primarily pro-con format." The for/against arguments are single short paragraphs to help you identify the key arguments.
