Two recent threads on Language Log, word classes and style guides, brought to mind one thing that baffled me when I began college teaching: FANBOYS. The first time I walked into our writing centre, I noticed that FANBOYS was pasted in large letters across one wall. While many readers may be familiar with FANBOYS, I'd never heard of them, but according to many freshman writing textbooks, FANBOYS is a mnemonic for the co-ordinating conjunctions in English (for, and, nor, but, or, yet, & so). Many style guides go so far as to state that when one of the FANBOYS is used to join two independent clauses, it must be preceded by a comma.
Of course, FANBOYS, as articulated above, is a myth. It is a myth in the sense that it is a fiction created to deal with a uncertain world in a simple way. It’s a myth in the sense that it is a belief that is shared by members of a certain community and, to a certain extent, identifies that community, the community being college composition teachers and their students (insomuch as each individual buys into the myth.) It’s a myth in the sense that it has taken on great import among the community of believers. And finally, it’s a myth in the sense it can serve a gate-keeping function, preserving power for those who know or “understand” it and denying it to those who don’t.
As the Cambridge Grammar of the English Language explains, only and, but, and or are prototypical coordinators, while nor is very close. So and yet share more properties with conjunctive adverbs (e.g., however), and "for...lack(s) most of the properties distinguishing prototypical coordinators from prepositions with clausal complements" (p. 1321). Furthermore, there are other ways to coordinate independent clauses in English.
So, where did this myth come from? Perhaps some influential author, reflecting their own personal preference, wrote something like: Where a clause is followed by a coordinator and a clause that could be either dependent or independent, a comma before the coordinator signals that the second clause is independent. This very limited observation could then have been over generalised. Yet, how one arrives at FANBOYS as a list of coordinators is difficult to imagine.
Whatever its origin, the myth, once established, seems to have become part of teacher lore and been propagated through other usage and writing books, their authors copying slavishly from those that came before. The reason for its staying power is clear: like any good myth, it gives the faithful a comfortingly simple handhold in a confusing world—in this case, that of composition. To paraphrase Knoblauch and Brannon in Rhetorical Traditions and the Teaching of Writing, it is extremely hard to teach students to be good writers; it is much easier to teach them the myth of FANBOYS.
In talking to many writing teachers, I have found that the majority of them, despite many years of post-secondary education, often leading to post-graduate degrees, were unaware of the myth of FANBOYS until they began teaching college composition. In a number of cases, they have told me that this led to a certain amount of anxiety. They wondered how they could have missed this rule. However, as they became acculturated into the college composition teaching culture, they internalized the myth and now many believe it to be both true and important for their students to learn. And so it goes...
[Update: March 2, 2012. An expanded version of this post is now available through the TESL Canada Journal.]
 Consider the change in meaning caused by the insertion of a comma before and in Karla Homolka’s post-prison statement in a Radio Canada interview, “I don’t want people to think I am dangerous and I’m going to do something to their children.” (July 5, 2005)
 In one example of such unthinking writing, Wong (2002) states, “each of the following coordinating conjunctions can link words, phrases, and clauses in parallel structures… and but for nor or so yet” (p. 365). So what individual words (that are not clauses) can be coordinated by so or for?