Say I wanted to write a new kind of etiquette guide, would it be legal to go through books by Miss. Manners and Emily Post to collect lists of social dos and don’ts and then rewrite them in my own voice?
I think it would. You can’t copyright ideas as such, only how they are expressed.
I suppose there are certain fields in which this principle does not hold, such as pharmaceuticals, where the ‘idea’ of a drug, i.e. its chemical formula, does have legal protection. But I cannot see how rules of behaviour could be protected in the same way. After all, in theory they are descriptions of accepted behaviour, and not new work by an author.
The “idea” of a drug is protected by a patent. Ideas about appropriate social customs are not patentable and therefore can only be protected by copyright. Change the wording and you are no longer bound by copyright laws.
Isn’t that I said?
Or are you just agreeing with me? In which case I said it first, and you owe me royalties.
I was agreeing with you, but just throwing in the bit about patents. Royalties are in the mail.
ETA: And until said royalties arrive, you have unlimited bragging rights.
Yes, the advice above is correct. Ideas are not copyrightable. You only can get in trouble if you lift text directly from other sources.
It would be good manners to credit your sources, however.
On second thought, why should I pay you royalties?? That idea you expressed was NOT copyrightable and since I changed the wording I owe you nothing. 
shakes fist
contacts pilots and crew of Enola Gay bomber and tips them off about unlicensed use of name
Patents protect products, not the description of them. So if a drug is patented, you have to pay for the rights to manufacture and sell the drug. However, you can write about the drug and its patent freely, e.g., in a journal article or in a reference book about drugs.
No, the phrase “Enola Gay” is too short to be copyright. It might be a trade name or trade mark, but I doubt that. The original use, to name a bomber, would not have been a trade name, since it was not used in “trade”. So no license fee would be payable.
You’re right, my whole joke was based on a misapprehension of copyright law. I’ll never make that mistake again!