Facts versus opinions
Facts are statements that are true and objective, for instance, something like ‘dogs are animals’. Facts do not generally need to be referenced, unless they’re not common knowledge, something which is discussed in the next section.
Other people’s opinions or interpretations, however, do need to be referenced, since they are someone else’s ‘work’, so to speak. Even if you have formed that same opinion in a completely independent manner, if you write someone else’s opinion down on paper then you must reference it. In this case, where you think the same thing, you might state your own opinion and then back it up with a quote and reference:
It would not have been possible for Japan to attack the mainland United States during World War II in any real capacity, due to the States’ large population, burgeoning industrial wartime production and the people’s willingness and capability to fight. The Japanese admirals recognised this fact: "You cannot invade America. There will be a rifle behind every blade of grass" [reference Admiral Isoroku Yamamoto].
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