As noted above, we always must give proper credit to those whose ideas and facts we are using. One general exception to this principle occurs when the ideas we are discussing represent “common knowledge.”. If the specific facts and figures we are discussing are assumed to be known by the readership, then one need not provide a citation. For example, suppose you are an American student writing a paper on the history of the United States for a college course. In your paper, you mention the fact that George Washington was the first president of the United States and that the Declaration of Independence was signed in the year 1776. Must you provide a citation for that pair of facts? Most likely not, as these are facts commonly known by average American high school and college students. The general expectation is that “everybody knows that”. However, suppose that in the same paper you must identify the 23^rd president, his running mate, and the main platform under which they were running for office, plus the year they both assumed power. Should such material be considered common knowledge? The answer is probably no, for it is doubtful that the average American student would readily know those facts without needing to consult an authoritative source (I had to look up the answers).

But, the question of what constitutes common knowledge is a little more complicated. Let’s take another example. Imagine that we are writing a paper and we need to discuss the movement of sodium and potassium ions across a cell’s membrane as described by the Martini and Bartholomew paragraph above. Surely, those ideas are not common knowledge amongst college students and if they were expected to use those concepts in a paper they would be expected to provide a citation. However, let’s suppose that the individual writing the paper was a seasoned neuroscientist and that she intended to submit her paper for publication to a professional journal. Would the author need to provide a citation for that material? Not necessarily. Although for the non-scientist the description of the concentration gradients of sodium and potassium ions inside neurons may look sufficiently complex and unfamiliar, the material is considered common knowledge amongst neuroscientists. It would, indeed, be shocking to find a neuroscientist or biomedical researcher who was not familiar with those fundamental concepts.

In sum, the question of whether the information we write about constitutes common knowledge is not easily answerable and depends on several factors, such as who the author is, who the readers are, and the expectations of each of these groups. Given these considerations, we recommend that authors abide by the following guideline: