Inductive Hermetic Theory

Dear all,

I have used some spare time to jot down some reflections about what I decided to call "an attempt at an inductive Hermetic Theory".

The basis idea is pretty clear. Ars Magica rulebook already describes the main principles of Hermetic Magic in chapter 7 and 9 with a wealth of details. However, when one starts to browse through the multiple exemplary spells reported in the rest of this last chapter, one quickly comes to the conclusion that other general rules, either expressed or implied, were used in the design of these spells. For instance, one may discover in the description of the spell Image of the Beast InAn 5 some precisions about the kind of possible Arcane Connections. The description of this spell indeed notes that “Wounds caused by an animal are an Arcane Connection to that animal with a lifetime of a few hours”.

Of course, the reader may decide to ignore these hints at a “more general truth” and decide e.g. that a wound caused by animal only creates an Arcane Connection within the context of the spell Image of the Beast, and that this would not be true in other cases. But what if it were? What if, for instance, a Magus wounded by an animal wanted to destroy it with a Perdo spell? Should the wound then not be treated as an Arcane Connection to the animal?

By following this line of reasoning, I tried to pinpoint some general rules not expressly mentioned in the rulebook but nevertheless “hidden” within the description of individual spells.

If you are interested in this exercise, feel free to have a look at where I summarise the results of this analysis and to leave me a comment!


I like it. There's a lot buried in the spell descriptions and bringing it out like this is good.

If anyone is feeling really ambitious, doing the same with spells from the various supplements would also be good. Any game with such an impressively large set of publications is going to have sprawl problems and something like your project is a good way to help deal with that.

Top notch stuff. Thanks for sharing this :slight_smile: I had not spotted quite a few of those.

However, most of this stuff belongs to "legacy" spells, so I am not sure if they should be considered "normal guidelines". I have special problems with adding a pair of magnitudes to cast the spell without gestures and voice penalties. This is a great guideline in any case, so I will forward your stuff to my troupe for reference. Thanks :slight_smile:


Good work.


I don't have my books at work but here's something else to think about: Without getting into whether this is because the Aegis is a special breakthrough or not, there is a line that says it's always case on the Winter solstice and so the spell is able to last a year. Does this mean that all Duration Year spells must be cast on the solstice? If an Aegis is not cast on the solstice, how long does it last? Can it be cast at all on a non solstice?


Nice! I like it. :smiley:

You probably want to make some corrections along the lines of The Fixer's comment. The animal skins used effectively do lower the magnitude since they allow an additional effect (stopping the spell) without increasing the magnitude, which is the same as saying they are of a greater magnitude then reduced using the animal skins. This puts it in line with the other "substantial requirements," not in disagreement with them. You'll want to remove the Muto comment lower on the page, too.

Also, you might want to reference the Sizes in RoP:M or HoH:MC for Muto. The effect isn't so special to Muto as it is to Size in the game.


I thought it was believed to make the spell more potent. I don't recall anything about duration having to do with the solstice.


Casting right after the solstice (either) or equinox (either) will cause the spell to last the longest.

The spell description says most covenants choose the day after Winter because many auras are stronger then.

Oh, ya, Year duration itself. :blush: Yes, either any equinox or solstice will do just as well.


Ah, nm then. I was reading it as if the solstice was special of itself. It's just they Year duration on a solstice/equinox just makes it last for the full year.


But why winter? Certainly not the most appealing of times to go about marching around your covenant, especially at the more northern regions.

Winter is the Christmas season and the most likely time of the year that everyone in the Covenant will be there. Remember that people need to be present at the Ritual, or they will count as a "guest" for a year....

I agree, this seems to be the likely reason why Winter is normally chosen. Everybody should normally be home.

but the sad thing is if you look at the penalty for casting a normal spell with a soft voice it is -5 and for no voice it is -10. So this modification of the spell makes no difference at all unless we take it to low levels where a magnitude is one level rather than 5. (which, come to think of it, is a pretty neat idea)