How to write a good introduction section. And tell if yours is bad.

The introduction section is an important part of any scientific paper. Introduction sections serve various purposes, but the most important is in my experience also the most often neglected: motivating your work. Explaining why you did what you did, in terms that others will appreciate. You need a good reason to do any research project, but many seemingly-good reasons actually are weak reasons.

Fortunately, help is available. I just found these mini-templates for how to write a good introduction section. (ht Brendan Nyhan) They’re from political science, but they generalize to ecology and other fields. For instance, one template is (i) This topic is important–>(ii) but something is missing/wrong–>(iii) and I fix it.

I only wish the author had included some mini-templates for bad introductions.

For instance, (i) Broad topic–>(ii) list-like review of previous work on that topic–>(iii) here’s what I did is a common bad introduction. Your introduction should not comprise a list of what other people have done, and your statement of what you did should not merely add to the list. This sort of introduction is like a martini glass with a hole in it. There’s no motivation, no logical link between what others have done and what you did. It’s not enough to merely show that whatever you did hasn’t been done before. There’s an infinity of things that have never been done before, and most of those things are not worth doing.

Want to figure out if your introduction lacks motivation? Here’s a test: if your introduction reads just as well if you swap out what you did and replace it with what someone else did on the same broad topic, your introduction lacks motivation. You can’t make this swap with a good introduction. For instance, if you follow the (i) This topic is important–>(ii) but something is missing/wrong–>(iii) and I fix it template, your introduction will stop making sense if you swap out your (iii) for other work on the topic that tries to fix some other problem, or that doesn’t try to fix a problem at all.

Here are a couple of other helpful exercises to help you learn to recognize a good introduction, and spot the motivational gaps in a bad one:

• Figure out what template fits the introduction of every paper you read this week. And if none of those templates are a good fit, figure out if that’s because it’s a bad introduction, or if it’s because the paper follows some other good template.
• Take a paper from, say, Ecology, and rewrite the introduction (and key results and conclusions) as the first two paragraphs of a Nature or Science paper–the abstract plus the first “regular” paragraph. You’ll probably find that there are whole chunks of introductory material in the original paper that you’ll want or need to discard during conversion. Which reveals that those chunks weren’t essential to the logical flow and motivation of the paper. Conversely, you may well find that the conversion doesn’t read well or has gaps in the logical flow, which means that the original paper omitted some key motivating steps, some key logical connections between paragraphs.

p.s.: the author of the linked piece is ok with introductions that begin with statements like “Ecologists have long been interested in…” or “Many ecologists have studied…”, which serve no useful purpose. Focus on ecology, not what ecologists think or say about ecology.