My favorite T-shirt says "I [heart] irony. It's a great shirt, because no one can be absolutely sure that I love irony. Maybe I'm ambivalent about irony and I'm wearing the shirt ... ironically. Despite what the Ethan Hawke character in Reality Bites may have said, irony is not as straightforward as meaning the opposite of the literal meaning of the words you are uttering. Rather, it's meaning something that is some distance from what those words mean -- a distance that some in your audience may be able to decipher, but that others may miss altogether.
What, you may be asking yourself, does this have to do with the issue of authorship of scientific papers?
I've blogged before about authorship issues, and recently it came up again in my response to an Inside Higher Education article in which Nicholas H. Steneck claimed that practices like guest authorship damage the integrity of the practice of science.
That, of course, prompted a flurry of comments about differing practice involving who gets counted as an author and who merely gets an acknowledgment. And these comments, I think, demonstrate that there is no consensus about what kind of contribution entitles you to be an author on the paper. Not only do different fields do it differently, but different research groups in the same field -- at the same university -- do it differently. What this means is it's not obvious at all, from the fact that your name appears as one of the authors of a paper, what your contribution to the project was.
I suppose there are possible worlds in which who is responsible for what in a scientific paper might not matter. In the world we live in now, however, it's useful to know who designed the experimental apparatus and got the reaction to work (so you can email that person your questions when you want to set up a similar system), who did the data analysis (so you can share your concerns about the methodology), who made the figures (so you can raise concerns about digital fudging of the images), etc. Part of the reason people put their names on scientific papers is so we know who stands behind the research -- who is willing to stake their reputation on it.
The other reason people put their names on scientific papers is to claim credit for their hard work and their insights, their contribution to the larger project of scientific knowledge-building. If you made a contribution, the scientific community ought to know about it so they can give you props (and funding, and tenure, and the occasional Nobel Prize).
But, we aren't in a possition to make accurate assignments of credit or responsibility if we have no good information about what an author's actual involvement in the project may have been. We don't know who's really in a position to vouch for the data, or who really did heavy intellectual lifting in bringing the project to fruition. We may understand, literally, the claim, "Joe Schmoe is second author of this paper," but we don't know what that means, exactly.
Don't get me wrong, irony is a perfectly lovely literary device in novels and short stories, but in scientific communication we might be better off with less ambiguity. Like a number of my commenters, I'm not wedded to the ICMJE definition of authorship as the definitive definition. However, I think that it exists because there is a real issue that needs to be addressed here: we need a clear way to figure out who is responsible for the scientific work in the literature. We can have a discussion about how to make that clearer, but we have to acknowledge that at the present moment, noting that someone is an author just doesn't do the job.
And here's where the issue of "guest authorship" comes up.
A guest is someone who is visiting. She doesn't really live here, but stays because of the courtesy and forebearance of the host. She eats your food, sleeps under your roof, uses your hot water, watches your TV -- in short, she avails herself of the amenities the host provides. She doesn't pay the rent or the water bill, though; that would transform her from a guest to a tenant.
To my way of thinking, a guest author is someone who is "just visiting" the project being written up. Rather than doing the heavy lifting in that project, she is availing herself of the amenities offered by association (in print) with that project, and doing so because of the courtesy and forebearance of the "host" author.
The people who are actually a part of the project will generally be able to recognize the guest author as a "guest" (as opposed to an actual participant). The people receiving the manuscript will not. In other words, the main amenity the guest author partakes in is credit for the labors of the actual participants. Even if all the participants agreed to this (and didn't feel the least bit put out at the free-rider whose "authorship" might be diluting his or her own share of credit), this makes it impossible for those outside the group to determine what the guest author's actual contribution was (or, in this case, was not). Indeed, if people outside the arrangement could tell that the guest author was a free-rider, there wouldn't be any point in guest authorship.
Science strives to be a fact-based enterprise. Truthful communication is essential, and the ability to connect bits of knowledge to the people who contributed is part of how the community does quality control on that knowledge base. Ambiguity about who made the knowledge may lead to ambiguity about what we know. Also, developing too casual a relationship with the truth seems like a dangerous habit for a scientist to get into.