So this entry on the Patry copyright blog caught my eye. That's a blog covering legal issues related to copyright. And it's definitely geared toward lawyers, whereas places like Groklaw try to make their legal stuff accessible to non-lawyers.
The reason why the question posted as the title is relevant is that the U.S. constitution grants Congress the power to extend copyright to authors. But the constitution doesn't define what an author is. At the time, an author would be pretty clear.
1 a : one that originates or creates : SOURCE
b capitalized : GOD 1 2 : the writer of a literary work (as a book)
In the 1700s, it was rare to have a group of people co-author a work and even rarer for them to care about the authorship of a work for economic reasons. Today it's a little more complicated. When you work for a company, stuff you write within the scope of your work is a work-for-hire, and the company is considered the author. Legally that is. I'm not sure I agree with that morally though. It's still my thoughts, effort, and inspiration that created the work.
When you have a small group, it's not a big deal to consider yourself a co-author. Does everyone have the same rights? Or does it mean you get to put it up to a vote within that group? What if the group become larger? I don't mean this to be a legal question. I'm pretty sure there's some guidance from the courts on these questions already so I don't much care what they think until I get into a legal copyright situation.