Previously in this series on how to write a scientific paper: ten tips for editing your sentences.
Now that you have revised and polished your draft and are the happy owner of a shiny new manuscript, one more step remains before you can submit it to a journal: writing the cover letter.
The cover letter is, in my view, mostly a historical remnant. Having to write one is, consequently, rather annoying. I can see that there may be some reason for cover letters for journals where the papers are too long to be skimmed by the editors, but even then, I doubt whether cover letters are of any use. Let me explain.
The point of the cover letter is to convince the editor that your manuscript is solid and important and that it fits their journal. But this is something that the abstract should do in the first place, especially if it follows the broad-narrow-broad formula outlined earlier in this series. The paper itself should do the job, too. In particular, the paper’s introduction should contain all the information that the editor needs to decide whether the paper is in the journal’s scope. It should also be enough for gauging whether the results sound believable and important enough for the paper to be sent to referees, instead of bluntly desk rejecting it. So why repeat all this information in a redundant letter?
So a big thank you to those journals who no longer ask for a cover letter.
Was I an editor, hard pressed on time, whose journal demands cover letters, I would highly appreciate a cover letter that is focused and short, say three to four paragraphs, max one page, preferably less. Here are two ways to write a short cover letter with only a few paragraphs and less than a page of text.
The better but slightly more adventurous way is to follow the inverted-pyramid schema that journalists commonly use for news stories. Most scientists are not used to writing this way! When following the inverted pyramid, you should begin with the most important thing and then proceed towards less important things, the nice-to-know details of the story, one by one and in order of decreasing importance. Tell what you have found in the very first sentence or two, then tell why your finding matters, and only then say something about how you obtained your results. Do not write a detailed explanation of your methods unless they are the key point of the paper; the editor is probably too busy to care, and if not, the details can be found in your manuscript. This way of structuring the letter is particularly suitable for those top-tier journals whose editors desk-reject most of the papers that they receive— they do not have the patience to search for the main point if it is buried somewhere on page two of your letter. They want to hear it first and then decide.
As a side note, the inverted-pyramid structure should always be used for press releases; those are read by journalists, not scientists, and journalists only get confused if they have to wade through lengthy introductory material before the main point arrives.
The other, more traditional way is to structure your cover letter in the same way as the abstract, or the Introduction section. Begin with the broad context, and then narrow the scope down and proceed towards your specific research question. After stating the question, tell what you have found out and how, and why what you have found out matters. But please be swift and move quickly: the first paragraph for context and question, second paragraph for the key result, and the third paragraph for significance.
You can also consider writing a hybrid version of the traditional cover letter and the inverted-pyramid lede. First, state your key result in a single-sentence paragraph: “In this manuscript, we show that X”. Then, follow the structure of the abstract and explain the context and the question in the second paragraph, a more detailed explanation of the result in the third paragraph, and an account of its significance in the fourth paragraph.
Whichever structure you choose, put emphasis on the implications and impact of your results. The why-does-it-matter part matters more than the how-did-you-do-it part, even if you have used particularly inventive methods. Do not exaggerate; rather, tell honestly what your work means. Whenever you feel like typing the word “very”, take a deep breath, command your fingers to stop, and jump directly to the next word.
Cover letter: if you have to write one, keep it simple, keep it short, put important stuff first, tell why your work matters.