How to Write a Research Paper in History/Citing your sources
The most important part of citing your sources is following your teachers' instructions and obtaining a copy of the correct style manual in its current edition. Style manuals vary widely amongst themselves and between editions. For example, the American Psychological Association made major revisions in citation style between the fourth and fifth editions. Do not assume that teachers in the same school use the same style manual. If in doubt, ask early in the writing process.
Learning a citation style well can be very useful, at least in a few standard forms. Memorizing the format for books and journal articles, for example, will probably mean you will not have to consult your style guide for the vast majority of your citations. This will save time (and misery) and allow you to concentrate more on the actual writing of the paper than on the formalistic aspects of citation.
Citation itself is very important for two major reasons. First is that citation allows you to give adequate credit to what others have said — this is important in order to ward off plagiarism and all of its evils, and is additionally valuable because "credit" is one of the primary currencies of academia (even if you don't regard it as such, your professor probably will).
Citation also allows the reader to know where your sources are located and what sources you have consulted—useful to your paper graders both in assessing both your argument as well as how much work you have done, and necessary in general to appreciate the value of a historical paper.
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