For currency. If you need current information, news outlets such as the New York Times and the BBC, think tanks, government agencies, and advocacy groups may provide appropriate sources for your research. When using Google, you can limit a search to the most recent year, month, week, or day.

For authority. As you search, keep an eye out for any experts being cited in sources you examine. Following the trail of citation may lead you to sources by those experts—or the organizations they represent—that may be even more helpful. You can limit a Google search by type of Web site and type of source. Add site:.gov to focus on government sources or filetype:pdf to zero in on reports and research papers as PDF files.

For scholarship. When you need scholarly or peer-reviewed articles, use a library database to look for reports of original research written by the people who conducted it. Scholarly articles provide information about where the authors work (such as universities or research centers), use a formal writing style, and include footnotes or a bibliography. Articles that are only one or two pages long are probably not scholarly. In the sciences, peer-reviewed articles can be as short as three or four pages; in other disciplines, articles may be thirty or forty pages long. Don't rule out an article just because it's long. Read the abstract or the introductory paragraphs and the conclusion to see if the source is worth further investigation.

For context. Books are important sources in many fields such as history, philosophy, and sociology, and they often do a better job than scholarly articles of putting ideas in context. Don't be put off by their length. You don't have to read every book cover to cover. You may find a single chapter or even a few pages that are just what you need.

For firsthand authenticity. Some projects can benefit from primary sources; in some fields, primary sources may be required. In historical research, a primary source is one that originated in the historical period under discussion or is a firsthand account from a witness. In the sciences, a primary source (sometimes called a primary article) is a published report of research written by the scientist who conducted it. For more information, see 52d.