My first real introduction to citations as being important was when a history teacher of mine in college was concerned that I'd committed academic dishonesty -- failed to cite a source for something she felt was obscure. After a nervous couple of minutes for me, we had a nice chat. What I'd done was to mention, without citation, Newton's prism experiment. I hadn't cited it because it was something I'd been seeing mentioned for years without citation, so figured counted as 'common knowledge' and not in need of a citation. My history teacher, on the other hand, had never heard of it before, so was looking for the citation to the person who had discovered the experiment (perhaps a citation to Newton himself; I now have the right book -- Newton's Opticks).
So that's one use of citations -- avoid annoying your teacher. Somewhat more generally, credit people for the work they do. That's an important thing in being a scientist, as the people you're giving credit to are your colleagues. Conversely, your colleagues will be peeved, to put it mildly, if you fail to credit them for their work.
The use at hand, as the title suggests, is to provide the backup for your claims. You could avoid some of that by providing full descriptions yourself, but then your article becomes impossibly long. Instead you can write something like "The earth is round and rotates.", where you then give the full address to 1 and 2 somewhere later in the document (in print media days) or hyperlink the words directly. An alternate that I prefer is to provide the direct 'who' and 'when', such as "The earth is round [
If you could read infinitely fast, it might be doable to simply read everything from everywhere. But for us humans, some means of trimming the candidates to manageable volumes is needed. So, for myself at least, if I'm trying to learn about a scientific topic, I head for scientific sources, or as close to the original as I can understand.
The bibliography/citation list is a quick way to figure this out. Places that are citing wikipedia articles, newspaper editorials, and so forth, for most of what they have to say are not strong sources. If the topic has scientific merit, there will be scientific papers on it. If I couldn't read, or would have a hard time finding and reading, the original scientific papers (which is true in most fields), then I want to be learning from someone who could and did. The strong source is one which is providing me the ability to go in to the literature and start learning about the particular part of the article which caught my attention.
This last is another important purpose of citation: It helps readers learn more. I would rather be learning the science from an author who is trying to help me learn it.
Now for the mirror test: How do my own postings hold up to that standard? In this post, it does ok, in the sense that this isn't about the content of science; it's my opinion of some things to consider in looking for sources from which to learn the science. In the science posts, not always as well as I'd like. So I'll take this post as a reminder to myself to include more references and links.
In my blogroll, two that are particularly good with their citations are Skeptical Science and RealClimate, though I think almost all are pretty good -- at least better than I.
c.f., I translate to myself as meaning 'See, for example'. It means that there's more than one source, and this is either the one that I used (though I know there are more), or that for some reason I prefer it.
Update: my self-translation is incorrect, see Nick and Peter's comments. What I really want is 'e.g.', for exempli gratia (free example is my translation here, unfortunately, it's my son who is the latinist.)
ca means 'about' (circa).