People sometime ask whether it's proper to cite blogs in a law review article. A few thoughts:

1. Crediting Ideas, Big or Small: Not only is it proper to cite blogs to credit them for their ideas -- it's mandatory, if an observation in your article was borrowed from someone else's blog post, or even just if the blogger had the original observation first. That's the same rule as when you borrow from a law review article, an op-ed, or even a personal conversation.

2. But Check with the Author: It's true that blog posts are often less thought-through than articles or op-eds. (They're also unedited, but many op-eds aren't substantially edited by editors, and certainly not by editors who have knowledge of the law; yet op-eds are certainly citable.) It therefore makes sense to check with the author before citing the post, in case the author wants to elaborate on it, or even recant it in some measure -- it's not necessary, but it can be helpful.

3. Supporting Authority: If, however, you're making an assertion that you want to rely on without proving yourself, and therefore want to cite supporting authority for it -- as opposed to giving credit to the originator of an idea, or referring to a particular counterargument that was seems to be present only in a blog post -- then you should cite a law review article or a book. Those are the sources that are more likely to be the more thought-through and detailed expositions of the argument.

4. Factual Assertions: Finally, you should not cite blog posts for specific facts quoted or paraphrased by those blog posts, whether they are facts about cases, statutes, social science data, or whatever else. Find, read, quote, and cite the original source instead. But of course that's true not just as to blog posts but also as to articles, books, and other sources -- if they are quoting or paraphrasing another source, you should go to the original. Don't let the intermediate source's errors and oversimplifications become your errors and oversimplifications.

Earlier this morning, I wrote:

It's true that blog posts are often less thought-through than articles or op-eds.... It therefore makes sense to check with the author before citing the post, in case the author wants to elaborate on it, or even recant it in some measure -- it's not necessary, but it can be helpful.

Tim Sandefur responded:

I must say I really disagree with the "check with the author" thing. Why? I never check with the author of a law review article or a book when I cite them. I can see that in some cases it might be helpful if you think the author could expand on some point, but that would probably be best done in a new post by that blogger.

When I cite a blog it is very often because I am citing someone whose views are contrary to mine, and if there were any point of etiquette that counsels me to ask permission or anything, that person would then refuse (or alter the blog post) and deprive me of a helpful reference. The fact that people can retroactively alter their blog posts makes it especially likely that a person who made a comment that later proves embarrassing will then try to weasel out of it when he's called on it in the form of a law review citation.

In my view, there's no more reason to request permission before citing in a law review than there is to request permission before linking to it from my own blog and criticizing it. If the person then chooses to alter the blog post or elaborate or whatever, that's fine, but why should I give him a chance to cover up his tracks before I criticize him?

Now, obviously blogs are, as you say, off-the-cuff, and they should be cited with that in mind (and if cited, should be read with that in mind). And you do say that there's no "rule" here, but I still don't think there's any reason to set out some guideline of etiquette that counsels any obligation on the part of a reader or writer to ask permission before citing a blog post. And I think there is an obvious downside in a bloggers' ability to go back and change his statements.

Here's my thinking: None of this is a matter of needing "permission" -- but it is a matter of making sure that debates are based on real disagreements, and not on misunderstandings, silly mistakes, or qualifiers that are omitted in the course of a casual conversation.

Say you say in a quick blog post, "Content-based speech restrictions are unconstitutional," and I have a paragraph in your article saying, "Some scholars argue that content-based speech restrictions are unconstitutional, but they're wrong -- after all, libel law, obscenity law, and many other constitutionally permissible laws are content-based." But you didn't really mean to argue that content-based speech restrictions are unconstitutional; you just omitted a "generally," or some other qualifier. What's the point of the back and forth? How does it help the reader, or the state of professional knowledge?

Or say you accidentally omit a "not" or an "un-," or make a similar typing error (not uncommon in quickly written prose). And say you don't notice this and your readers don't tell you (maybe you don't have a lot of readers who help you by sending corrections, or maybe they just weren't paying attention to this post). I then write "X says that content-based speech restrictions are constitutional, which shows what a minimalist he is when it comes to free speech" -- but it turns out I'm arguing not with your sincere beliefs or your edited prose, but with your slip of the finger. What's the point?

Nor is there much reason to worry, I think, about the person "covering his tracks" by modifying the post. If the original post is somehow especially telling, you can always cite the original (just save a copy of the original version, and note in your footnote that you're citing to the original version and not the updated one). Thus, for instance, if you think the original post really reflects the speaker's true views, and the revision is an attempt to disingenuously hide the beliefs that slipped out in a rare moment of candor, go ahead and cite to the original.

But if the person e-mails back sincerely saying, "Thanks -- I misspoke, and I've corrected the post to more accurately reflect my views [or the state of the law]," then what have you lost? At most the opportunity to engage in a debate with a view that might not actually be held by anyone, or to represent the post as your target's true views when it's actually just an error. Pat yourself on the back for being nice, and, more importantly, for sparing your readers a pointless debate against a view that even your target doesn't actually hold.

Now some of this is specific to law review articles that cite blog posts. If you're citing an article, you can be more confident that the author really means what he says there, because the author has likely reread the article several times, and confirmed that he didn't just misspeak. If you're writing a blog post that cites another blog post, you might not want the delay that often accompanies such queries. But if you're writing a law review article, you have the time to check things, and good reason to avoid needless debates.