The most common type of source you are likely to encounter is a secondary source. A secondary source is any source about an event, period, or issue in history that was produced after that event, period or issue has passed.
Aside from a textbook, the most commonly assigned secondary source is a scholarly monograph - a volume on a specific subject in the past, written by an expert. Also common are articles in scholarly journals, which are similar to monographs, but on a smaller, more focused scale.
Scholarly monographs and articles are very useful sources. Written by experts, they come with a certain built-in "credibility"; articles are often peer-reviewed, meaning that they were judged worthy of publication by other experts in the field prior to going into print. Similarly, books and monographs go through elaborate pre-publication editing processes to ensure a minimum of factual errors.
Despite such precautions, however, it would be a mistake to believe that a secondary source, even if written by the most reputable of academics, is necessarily "reliable" by mere virtue of its pedigree.
Good questions to ask of any secondary source are the following:
For additional tips on how to approach a secondary source, consider the questions listed in our section on book reviews, Here, let us simply close with the following:
Notwithstanding the skepticism you should bring to any text you read, you can generally assume that secondary sources assigned for college classes are solid resources: they are written by acknowledged experts in the field, they often review the historiography of their subject up until the date of their own publication, and their authors base much of their arguments on their own study of primary sources relevant to their field. Indeed, one possible definition of a secondary source is that it is a piece of scholarly writing that comments on primary sources. To find out more about primary sources, click here.