When you’re conducting research for an essay, a debate, or a report, you will often come across multiple sources of information about the same event or topic. How can you tell which of these to use?

One of the most tried-and-true methods for “ranking” information is to distinguish between primary and secondary sources.

A guide to research published by the University of Maryland says that primary sources “are from the time period involved and have not been filtered through interpretation or evaluation. Primary sources are original materials on which other research is based.” Examples of primary sources include things like eyewitness accounts, photographs, newspaper articles from the time and place you’re researching, and physical objects (bones, pottery, coins, and so forth).

Primary sources are considered the gold standard in all academic research, as well as in journalism. The reason is simple: if you get your facts second-hand, you have no way to be sure that they’re accurate.

Secondary sources do have uses though. Encyclopedias like Wikipedia are considered secondary sources; they pull information together from primary sources to give an overview of a topic. In this way, secondary sources can help someone to learn the basics of a new subject. These kinds of sources are also great places to get commentary and analysis, because they often draw from multiple viewpoints or discoveries and make connections between ideas.

The quality of a secondary source can be tough to judge, which is why citations are so vital. If there are references, then the reader can go back and look at the primary sources that were used to find out whether or not the secondary source is accurate.

A simple example is Wikipedia’s entry for “primary source.” The first sentence of the entry says, “Primary source is a term used in a number of disciplines to describe source material that is closest to the person, information, period, or idea being studied.” After that, there appear two citations: one links to the University of Maryland’s definition. You can go to the original definition and see that although Wikipedia’s wording is slightly different, the idea is accurate. You can be confident in this case that Wikipedia didn’t just make it up or leave out important information.

As the entry goes on, it offers more citations – 31 in all, plus links to other outside sources, similar entries, and so on. This robust suite of references is what makes Wikipedia a valuable tool, because you can find hundreds of primary sources collected in one place.

Your professors have probably warned you against citing Wikipedia. They’re right to do so, but not because Wikipedia is deceitful or inaccurate (it does occasionally make mistakes, but so does everyone). The reason you shouldn’t cite it is that it is academically lazy not to read the primary sources for yourself.