Arnold Zwicky at Language Log has a fine, detailed post about the reasons for the absurd “rule” about not starting sentences with and or but, the No Initial Coordinators (NIC) rule. As he says, “A point of usage and style on which Liberman and I and the AHD and the MWDEU stand together with Brians and Garner and Fiske (and dozens of other advice writers) is, truly, not a disputed point. NIC is crap.” He speculates, sensibly in my view, that it originated in attempts by elementary-school teachers to get their kids to stop stringing clauses together in the monotonous fashion that comes naturally to them: “It was cold, and my mom made me put on a coat, and I went outside and I saw two dogs, and they…” He comes to this depressing conclusion:
Once NIC is out there, it will persist. Any fool with a claim to authority and either students or a publisher can get a rule ON the books, but there is absolutely no mechanism for getting rules OFF. People think that rules are important, and they are reluctant to abandon things they were taught as children, especially when those teachings were framed as matters of right and wrong. They will pass those teachings on. They will interpret denials of the validity of such rules—even denials coming from people like Garner and Fiske, who are not at all shy about slinging rules around—as threats to the moral order and will tend to reject them. I’ve had some success convincing some students and friends that some of the rules they were taught are not good rules to live by—but my success depends on their willingness to listen to me and their willingness to question their beliefs, two qualities that are not widespread in the general population.
(Here‘s his first post on the subject, “If they do it too much, they should be told not to do it at all.”)