“I don’t want them getting my home address, so to speak,” to paraphrase several characters in the Familiars and Familiars Generations series. Using a real name, one that is linked to a person directly, is considered a Bad Idea. Names have power. Thus magic workers and some key nulls take on use names. These are not fixed, as several characters in the Familiars and Familiars Generations stories show.
Some go farther, changing their names completely if they no longer fit. This happens twice this far in the series – Arthur and Jude. André/Garry is another possible case, although he does not legally change his name to André Lestrang. For one, the paperwork mess with the military would be epic. For two, his family would start asking questions he’d prefer not to answer. And having an everyday name as well as his on-duty name and use name is another buffer and deflection. Arthur changed his name to one that was not related to his original “outside the clan” name after he and the others fled to the Riverton clan. His old name no longer fit, at least in his mind. Arthur was different, and so what if it didn’t “match” a Hispanic last name? “Pisicagheara,” claw of the cat, also better fit his way of fighting and personality. He’s the concealed blade, the weapon hiding in plain sight. The younger Hunters, well behind his back, came to call him the Dark One for his style of dress and his personality. Well behind his back, in whispers, with a look-out posted.*
Jude is estranged from his family, so to speak. He truly is dead to them, blood price paid, and so keeping the family name doesn’t make sense. Jude – the patron saint of hopeless causes – fit him better, or so he felt. He still does. His last name, Tainuit, is a long-disused name meaning “solitary” or “outside.” His use name as a Hunter died with Karol, his old self, so he uses “Tenebriu” meaning “one in shadow.” His Familiar’s name, “Pasaru” translates “bird.” It has no specific use as a name per se, so it provides further deflection. “Shoim” in the clan’s speech can refer to a type of hawk (not a harrier), which should have been a CLUE. It was for Arthur. Jude wasn’t in any condition to realize how odd that was, and by now, Shoim just refers to his Familiar. (At the rate things are going, Shoim may become one one of the words Jude uses when, oh, he drops a carton of eggs or when Martha’s car dies at a bad moment.)
Thomas Arthur “Art” uses “Letters” as an inside joke. Arts and Letters often refers to a subdivision of a university, as in “College of Arts and Letters.” Mike grabbed “Red” because it was short, fit his coloring, and easy to recall. However, Rich managed to point out that it was also blatantly obvious and tied to him. So Mike uses “Defender,” something which caused both Arthur and his brother to raise their eyebrows in the lead up to the Terrible Hunt. No, Mike doesn’t know anything about the Hunter clans aside from what André and Lelia have told him. Morgana’s use name was also an inside joke, requiring someone to have the Arthurian word of Morgana Le Fey and the Lady of the Lake in mind. Deborah’s use name translates “flat-leaf parsley.”
*He probably knows anyway, since he’s Arthur. He’s the intelligence officer for a reason. But of course he’d never let the youngsters know that he knows. Because he’s Arthur.
Cat Rotator's Quarterly 
I keep worrying about how magical infosec is supposed to work. Should magic users ever mention their (or others’) use names outside of a circle? Introductions of the form “Hi, I’m Dave, use name Grelber” always seem wrong to me.
I’ve been rereading the Familiars novels, and there was a comment when Andre and Lelia met Mike (for the second time). Use of names outside of workings is Not A Good Idea. Makes sense because of familiarity issues.
When Andre and the others openly give their working names, it is always in a controlled situation (the shadow workers meeting, or when they are away from others and cross paths with two other known shadow mages.)
I remember when Arthur called Lelia “Mrs. Grey” which fits into the use of “use-names”.
Nice fill in and explanation of the working names vs. actual. Thanks!
Presumably any connection between ‘Actual Name’ and ‘Use Name’ should be one-directional – i.e. it is a lot easier to get from the magic user’s ‘Actual Name’ to their ‘Use Name’ than it is to go in the other direction.
Although no apparent connection between the two at all may be the ideal, as even a one-directional link can be cracked by someone nefarious who knows enough magic users and is willing to take the necessary time to check if there’s a link between any of them and a ‘Use Name’ they’ve come across.
It is fascinating to me how big a fictional universe you build so that your stories stay consistent and logical throughout the whole series.
Re: what Arthur knows or doesn’t know. Arthur being Arthur, he’s probably well aware of the truism that one good way to keep your enemies off balance is to make them think you know more than they want you to… and one good way to do that is to actually know more than they want you to.