The H-Teach List is having a really in-depth discussion on plagiarism. The general consensus is that the US plagiarists generally know they are being naughty, but Doug Deal asked an interesting question about most textbooks

Textbooks have a lot of written materials and lists of “suggested readings,” but as far as I know, they don’t usually have footnotes or endnotes or works cited. they don’t cite specific sources for the information or the analyses they contain. Why not?
The lecture presents an oral version of the same problem. We undoubtedly could cite sources for some of what we say in every lecture, but typically we don’t, or at least we don’t do so scrupulously. Is that okay too?

That is, many of our lecture Powerpoints for the classtoom tend to present facts “as-is” and not delve too deeply into where we got our information. To give some people credit, some lectures and textbooks do include citations (and I try to squeeze them in), but it’s rarely a key feature in the information most people see.
By the way, it’s not just the classroom. Most popular non-fiction, news stories and informational Web sites hide or eliminate citations. Why does it happen? Basically to simplify presentation for the audience. In a teaching situation, it may be the case that students don’t care where you got your Welsh data from…just that they have to memorize it.
Another problem many instructors/news providers may encounter is that many younger or less-advanced students usually don’t want to hear “maybe this or that”. I know I didn’t want to hear about it when I had one of these classes as a junior. In the beginning, students usually want to hear about one method/story and be done with it.
For instance, if you asked “how many sounds does English have?” I bet you don’t want to hear the linguist state “It depends on the dialect…” (even though it does).
So…how do we train students to care about citations? We can use the traditional stick method (it’s the one I mostly use). Problem Based Methodology would say that practicing research would teach students the importance of citations. That would probably help.
Here are some things that have taught me to love citations

1. Sometimes I need to look up a data point back up (usually an Old Irish verb form in my case). Citations really narrow the search process down quite a bit.
2. The stories I hear about people trying to figure out where different ancient authors really got their information makes me appreciate citations more. When reading ancient travelogues with crazy third-hand stories, you really do wish they had included a citation somewhere.
3. And it does help to have other sources to back up your kooky idea. It’s not just YOUR kooky idea, it’s just a minor extension of {citation here].
4. Finally, I like to look up other people’s data points (usually Fula verb forms) to see if any strategic editing has been done. Are ALL the data points included? Is ALL the text quoted? The answer is maybe not. In fact I’m downright paranoid about using other linguists’ data…I usually prefer to go straight to the original non-linguistic grammar or text.

It’s this last point that made me really understand the importance of looking up the original source and how important an honest citation is. It’s only when you can look at and TRACK several sources that you can begin to filter out unconscious bias.