The only source material that students may use in their projects without mentioning the resource is the information that is considered common knowledge and is therefore not attributable to a single source. Common knowledge is data that is usually known to educated people.
Among them, widely known dates and facts, and more seldom, language or specific concepts. On the contrary, any ideas, facts, and language that are original and peculiar products of a concrete person’s work are not considered common knowledge and must always be cited.
Sometimes, figuring out if particular information is common knowledge is tricky, so it is always recommended to cite a source if you are not sure that the data is common knowledge. If you mistake on the side of caution, the worst result would be that our teacher would tell you that there was no need to cite; but if you do not cite, there is a probability of ending up with a bigger problem.
If you have seen specific information in numerous sources but still think you should cite it, refer to the source that you think is most trustworthy, or the one that has affected your thinking the most.
Further, we will take a closer look at three main categories of common knowledge.
Widely known facts
Widely known scientific laws and historical facts — such as Einstein’s famous equation E=mc2, or that George Washington was the first president of the USA — are considered common knowledge. Therefore, students are allowed to include such information in their papers without referring to sources, and it will not be counted plagiarism. There are also facts counted as common knowledge that is widely known to specific groups of people but probably not to you. Still, you do not have to cite such facts. On the other hand, when you go into details and provide claims that are products of an individual’s thought, research, or analysis, you must cite.
Ideas or interpretations are not counted common knowledge, except the widely held ones
If you read in R.A.C. Parker’s history of World War II that British Prime Minister Neville Chamberlain should not have agreed to the 1938 Munich Pact with Hitler, and that he would have better selected another path, you would have to refer to the source, because this judgment is Parker’s theory, not a widely agreed-upon fact.
Nevertheless, there are certain opinions and interpretations that are considered common knowledge and do not require references. For example, if you write in your paper that the culture provides a means by which people adapt to their environments, you do not have to include references to this claim, as it is universally held by anthropologists. But, if you were uncertain that this theory was the generally accepted opinion among anthropologists, it would be better if you simply cited the source.
Verbatim language drawn from a source is not considered common knowledge, except the widely known formulations
You must always refer to the source when including a quotation in your paper. The rare exceptions to this rule relate to generally known quotes that have entered the realm of common knowledge.
For example, if you create a paper about President Trump’s Inaugural Address, you should cite the source for each quotation included in the paper. But if in your essay you compare one of President Trump’s lines to this commonly known phrase from John F. Kennedy’s Inaugural Address, “Ask not what your country can do for you — ask what you can do for your country,” you do not have to refer to the source of that single phrase. But, if you are analyzing Kennedy’s speech substantively and quote other lines, then it is necessary to cite every quote. Generally, if you are uncertain if a particular quotation is a common knowledge, provide a reference for it.