Proper citation of the sources that influence your work is foundational to good scholarship. All the academic work you do builds on the work others have done before you, and lays further groundwork for those who will come after you. When you write a paper, you are orchestrating a conversation about a topic that interests you. Your conversation partners are, on the one side, other scholars who have written before about related topics, and on the other side, your readers, who are interested in joining the conversation you’ve begun. Properly citing your work is your way of introducing your readers to the other scholars in the conversation. It also creates a “road map” of the topic you are exploring, so that your readers can find further information they may need in order to pursue the ideas that arise for them out of the work you present, and thereby add to the conversation themselves.
There are two kinds of sources with which you will find yourself working: primary sources and secondary sources. Both kinds need to be cited whenever you use them.
A primary source text is one about which you are actually writing. A primary source text might be the Bible, another ancient source, an epic poem that is the main topic of your paper, a journal article for which you're writing a response paper... anything that serves as your primary interlocutor (conversation partner) on a given topic. If you are writing a paper about Satan’s association with snakes in popular culture, for instance, some of your primary source texts might include the books of Genesis and Revelation in the Bible, the Harry Potter books, and the Disney movie The Jungle Book. (Note that a “text” does not have to mean a book or other type of printed word; it can also refer to movies, TV shows, video games, songs, etc.)
A secondary source text is one that, like your paper, reflects on a primary source text. Secondary source texts help you learn facts about primary sources that you didn’t know, or think about primary sources in new ways. Secondary sources for that paper on Satan and snakes might include a biblical commentary that will provide you some background information on Genesis 3, an interview with J. K. Rowling about the historical and cultural influences that helped her create Voldemort’s sidekick Nagini, or a journal article on the symbolism of snakes in children’s movies.
Additionally, of course, proper citation gives credit where credit is due. As such, it is an issue that goes to the core of your academic integrity: not to cite your work properly is to risk plagiarizing the work of another. You should cite another person’s work:
1. Whenever you quote someone else’s words directly.
2. Whenever you refer indirectly to the contents of a primary source text. Citing the specific author(s) to whose work you refer, even if you aren't quoting them, provides your reader with clarity about what you’re trying to say.
3. Whenever you refer, either directly OR indirectly, to a specific idea or approach to a subject that is someone else’s innovation. If you did not know a piece of information before you read John Smith’s book, you should cite him if you refer to that fact in your work. If you had never thought about the topic in exactly that way before you read Mary Jones’s article, you should cite her if you refer to that particular way of thinking about the topic in your work.
4. Note that, if you are writing a paragraph that engages two different ideas by the same author, or several different lines from the same poem, you don’t simply cite the overall text at the beginning or end of the paragraph. You must give a new citation every time you reference a different section of a text or a different idea within a single book. So, if you write one sentence that refers to an idea on page 77 of Dietrich Bonhoeffer's The Cost of Discipleship, and then you write a second sentence that refers to another idea on p. 83, you need to give two citations, each with the specific ideas you’re referencing — not just a single general citation of The Cost of Discipleship at the end of the paragraph. Likewise, if you quote something from p. 358 in a journal article, and then later in the same paragraph you refer to an idea from the same article that occurs three pages later, you need to give two separate footnotes for that article. Remember that you are creating a “road map” so that your reader can go back to your sources and find out more if s/he needs to do so. General citations, like vague maps, are not as helpful as specific ones.