Somehow I am on the mailing list of the University of Chicago Press, which informs me that the 18th edition of The Chicago Manual of Style is now available. I was surprised at the number, but find that the last one I purchased, more than 40 years ago, was the 13th edition. At the time, I had the 12th edition (1969).
In those days, I worked as a copy editor, and the manual was one I used a good deal. I preferred it to the Government Printing Office (GPO) Style Manual. But I started to wonder about my reliance on it, when I encountered
Never mind the Manual--it isn't holy scripture; I haven't joined a religious sect and taken an oath to be ruled by a book.
in Jacques Barzun's essay "Dialogue in C-Sharp" (collected in A Word or Two Before You Go).
And now I think my copies of the Manual of Style are long gone. I have moved three times since I bought the 13th edition, we have lost books to plumbing failures, I have occasionally and reluctantly purged my shelves, and no doubt the manuals were among those that were misplaced, drenched, or given away. The GPO Style Manual I know I had twenty years ago--I brought it to the office to show somebody the excerpt from John that leads off the foreign-language sections. But no such memory attaches to the Chicago manuals.
I have not edited for pay in many years. The books left over from those days are an early edition of Fowler's Modern English Usage, Gowers's The Complete Plain Words, Graves and Hodges's The Reader Over Your Shoulder, maybe the Fowlers' The King's English. But the best practical advice, in some ways, appears in Stendhal's autobiography The Life of Henry Brulard, as the advice he wished that he had received from Count Daru when young and first working in the imperial bureaucracy:
When you have a letter to write, think well about what you want to say, and then about the shade of reproof or of command which the minister who will sign your letter will want to convey. When you've made up your mind, write boldly.