Scholarly works are set apart from other types of writings by the use of citations. An essay on natural history might cover a scientific topic, but it is just an essay until it contains citations. Scientific papers are not scientific without citations.***
***This blog post is certainly not scientific...no citations here. OK, maybe one.
Most scientists do not question the need for citations nor the role they play in the paper itself. When we do not have a common understanding of the role of citation, we have trouble determining when citations are improper and what to do when what we think to be true shifts.
Most of us think that the big debates about citations is formatting. Do we number our citations or list the authors and dates each time? There are deeper issues that that. They have nothing to do with formatting.
The first time I really thought about citations is I remember that Stephen Jay Gould once got into trouble for citing a paper in his thesis that was not contained in his school's library.* His advisors questioned the link between the statement he was making and the original citation. They were not refuting that his statement wasn't true. Only that he didn't know it was true, because he could not have examined the original source. Another author's judgment on the assessment of truth was insufficient. That's how rigorous citation can be.
*This is a place where a citation is really needed. But, I can't remember which of his books I read this in. Structure of Evolutionary Theory? Panda's Thumb? I'm fuzzy on the details here, but whether it happened or not, it could have happened, which is all that is necessary here.
When I think about how I use citations, I feel there are two types of citations that I use.
The first I call vertical citations.
Vertical citations are the links between what has been found to be true in the past and a statement we currently would like to make to establish the truth.
For example, here is the first sentence of a paper that I just submitted to a journal:
There are approximately 1 billion cattle in the world with cattle populations steadily increasing over the past few decades (Estell et al. 2014).
This is a vertical citation. I am going back into the literature to provide evidence of the truth of a statement. I personally have not counted how many cattle there are in the world. Nor have I determined whether cattle populations are increasing or decreasing over the past few decades. So, instead of going out and counting cattle, I cite a paper that has established this to be true or has cited the papers that have established this to be true. The paper I chose to cite is Estell et al. 2014***
***et al. stands for et alia (in the neuter form), which means and others in Latin. Et alia is almost always abbreviated et al., which is funny because we really aren't saving that many characters. Really just one. I think, in part, it gets abbreviated because the actual Latin phrase depends on whether the "others" are male, female, or both. Easier to write "et al." than determine whether et alii, et aliae, et alia is more appropriate.
So, when are vertical citations necessary?
Any time we make a statement in a scientific paper about what we consider to be true outside of the personal experience we are describing, a citation is necessary.
If we want to say that there are a billion cattle in the world, we need a citation. If we want to say that atmospheric CO2 concentrations are increasing, we need a citation. The sky is blue? Citation. Gravity exists? Citation.
Now, if we want to say that we performed a certain procedure in an experiment, we do not need a citation. We hold it true that we might have measured something at a certain temperature, but there is no citation for this since it comes from our experience, not the literature.
Vertical citations go back into the literature to provide justification for the truth of statements we are making. Think of the Newton's phrase, if I have seen further, it is by standing on the shoulders of giants...When we cite a previous work, we are placing our foot on the shoulder of a giant that has come before us. We are reaching down vertically to build something taller.
As opposed to vertical citations, there are also horizontal citations. Like vertical citations, they reach down into the literature to establish the truth, but the purpose is different.
Horizontal citations are primarily for context. In the introduction, horizontal citations are typically used to identify intellectual tension. Study A found this. Study B found that. This and that cannot be both true under our current intellectual framework. We cite these papers to show what other researchers have found to justify our work.
In the discussion, horizontal citations are used in a similar manner, but it is not to establish that there is intellectual tension, but to see if there is intellectual tension. Study A found this. Study B found that. We found this, too. Therefore, it seems like this is more likely to be true than that.
With horizontal citations, we are not citing other giants, but instead other dwarfs (or other Isaac Newtons).**
**the original metaphor was "dwarfs standing on the shoulders of giants". Citation here. We think of Newton as a giant now, but originally he would have been a dwarf in the metaphor.
So, when I think about how I reference the literature, it is generally vertically or horizontally. I am either reaching down to stand taller, or reaching across to build linkages.
That's probably a long enough post for now. Down the line, I should cover the consequences of failing to cite the literature correctly and the consequences of determining that the findings of a published paper was not true: what happens when a giant tumbles?
Mostly as a note to myself, comparing legal citations and scientific citations is also instructive. The law only cares about what was legally true at the time the law was being examined. Science cares about what is known to be true at the time the scientific fact was established and after. Hence, changes in the law and changes in scientific understanding have much different consequences.