There are 3,000 ways to cite source material. One of the many explanations that there are so many styles is simply that many have been in publication for generations. Over time, distinct disciplines in academia have come to prefer certain citation styles over others.
One reason that it seems that the number of citation styles is so diverse is that of the choice of different formatting systems within the same style. One reason we cannot have only one consistent citation style is that each academic paper can appeal to an immensely different audience than another.
You have to cite everything you use, even if it’s common factual information like the dates of world war ii or the date of napoleon’s death.-a good explanation of common knowledge comes from the purdue university online writing lab (https://owl.english.purdue.edu/owl/resource/589/02/): generally speaking, you can regard something as common knowledge if you find the same information undocumented in at least five credible sources. additionally, it might be common knowledge if you think the information youre presenting is something your readers will already know, or something that a person could easily find in general reference sources. but when in doubt, cite; if the citation turns out to be unnecessary, your teacher or editor will tell you.