Not an assumption. Absolutely implied, no question about it.
Right, but that is irrelevant. The quote tells you that. Look at what it says about men getting pregnant. It specifically states this is a consequence of the character's essential nature not being changed. So we know: essential nature remains male --> cannot become pregnant even if shape changed into a female.
No, not really. You can effectively disguise essential nature, but not actually change essential nature. Here is what the core book actually says:
A thing’s essential nature cannot itself be changed. While Hermetic magic can completely change the way a thing appears, it cannot affect what that thing is.
So we know: Hermetic magic on a male --> essential nature remains male
Absolutely not in canon. Look a the steps:
Hermetic magic on a male --> essential nature remains male --> cannot become pregnant even if shape changed into a female.
This is rock solid in canon. What is not rock solid is a female taking the form of a male and impregnating someone. But we can probably assume the same holds the other way around.
The changes by the Persona Ability (HoH:S p.89 box New Supernatural Ability: Persona) "are total, proof even to the most intimate mundane scrutiny, but do not change the character's essential nature. Consequently, all Characteristic scores remain unchanged, Virtues and Flaws are transferred to all new forms, and a male character cannot become pregnant when adopting the persona of a woman."
Hermetic magic can violate essential nature for some time. See ArM5 p.79 The Limit of Essential Nature: "Any magic which violates a thing's essential nature must be maintained, and when power is no longer supplied the thing returns to its natural state. Thus, Muto magic must always be maintained, ..."
Arguing limits of Muto magic from the Persona Ability doesn't work.
Arguing e. g., that ArM5 p.89 "A thing's essential nature cannot itself be changed." excludes temporary overrides which violate the (HoH:S p.89) restrictions of Persona would exclude also changes to Characteristic scores and thereby transformation spells like Cloak of Black Feathers.
Without any breakthroughs, I imagine the best hermetic magic can do is something similar the story seed in page 37 of Art & Academe.
What I mean this is that you might have to get some donor spermae and maybe a really creative Muto spell that is able to make something that acts like a vat that holds the homonculus for nine months. The obvious downsides to this (1) it requires donor spermae (2) this spell would be creating an artificial womb rather than a true womb and (3) the babies that you birth might not exactly be human.
Thankfully, unless you are already sterile, you already have access to one half of the spermae already required.
Edit: It seems I've accidentally replied to OneShot. My bad!
Your essential nature is quite clearly not overwritten, as it remaining the same is explicitly why Corpus spells still work on you. Read my quote again, talking about the masking rather than actually changing essential nature.
But your underlying Characteristics are not simply modified. They still affect your final form, so they still exist in some way. Still, the real question is if Characteristics should have ever been included in the "consequently" statement at all since Hermetic magic can change them permanently.
As for sex, the core book does explicitly say, "Men are essentially male, and women essentially female."
ArM5 p.89 states "A thing's essential nature cannot itself be changed." This still allows to temporarily overwrite features of one's essential nature by Muto.
That the Persona Ability "does not change a character's essential nature" means, that it does not overwrite any features of it even temporarily. And from there HoH:S p.89 argues, that "a male character cannot become pregnant when adopting the persona of a woman".
This limitation of Persona does not address the possibilities of Muto magic at all.
A thing’s essential nature cannot itself be changed.
Men are essentially male, and women essentially female
No matter the apparent gender change, you cannot actually change gender via Hermetic magic. Period. You can make a male have female traits and vice versa, which is how you can violate essential nature. But you cannot change that essential nature.
Meanwhile, a canon consequence of the essential nature of being a man is not being able to bear children. That's not a trait, but explicitly based on essential nature even when all the traits have been perfectly changed.
Ok, so we have the argument involving HoH:S p.89 Persona out of the way, right?
ArM5 p.79f "Men are essentially male, and women essentially female" is quite another argument. So the troupe will have to determine, what exactly makes a person "essentially male" or "essentially female". It makes sense if they determine, that a person being "essentially female" cannot be changed by Muto to generate fertile semen.
I never made a single argument based on Persona. I don't know why people have fixated on something I didn't say. I made an argument based on a statement that happened to be written in the box about Persona. That statement is that a consequence of the essential nature of being male is not being able to become pregnant.
Meanwhile, the core book says Hermetic magic cannot change essential nature, and a man is essentially male.
Because the consequence of the essential nature of being male is not being able to become pregnant -with Persona-. Not Muto magic, since muto can overwrite from some time essential nature.
Oh, I missed you commentary on De Physica.
Interesting. So if the father is the cause of the child (until when the child is a consequence tied to the father ? That is still a question), then a woman cannot conceive in male form. BUT a man could easily transform into a woman to bear the baby of another man (or his own).
No. That's not what it says. You don't have a different essential nature for each effect on you in Ars Magica. There is no Persona essential nature v. Muto essential nature v. other essential nature.
Persona cannot change essential nature. Since it cannot change essential nature, it cannot change that essential nature of male prevents becoming pregnant.
Let's be clear here. Muto can hide essential nature, but it cannot change essential nature. Since a a part of a person's essential nature is to be human and Corpus affects humans, this means MuCo(Fo) to change a person into something other than human does not change the person from being essentially human along with its consequence of being affected by Corpus magic. Muto cannot change something essentially male to being essentially female. It can change body parts to make someone essentially male seem female.
Did you also note the wording in both Hermetic effects? Neither example lets a male become a female. One lets you adopt some physical characteristics. The other says it's just an apparent change of sex. And we might note on top of this that even a perfect change of all physical characteristics that doesn't change essentially male is insufficient to allow pregnancy.
The whole point of muto is temporary change. The core rule book also says one is essentially human. Part of being essentially human, is not being killed when someone hits you with a newspaper. If a Muto spells turns you in to a fly, you will likely die when you are hit with a newspaper, and that is how it's meant to be.
If Muto can give someone the ability to breathe air like a fish, fly like a bird, vision of an eagle, the ability to be squashed like a bug, etc, it doesn't seem a big step to say it can change someone's sex and have all the parts work. Male to female, clearly the spell would have to be a ritual with a duration of a year, however, female to male, I think we are overthinking what should be a standard Muto thing.
Notice that could can ReCo this fire to move it, you can PeCo this fire to kill it, etc. Why? Because even though you have changed the features of the person to seem to be like a fire, you cannot change the essential nature (person) via Hermetic magic.
No, that's not an essential part of being human. I'm calling BS on this. You can be wounded by a newspaper, even paper that hasn't been magically enchanted.
Do I really need to quote the rules from the book that nearly explicitly say you cannot use Hermetic magic to turn change the essentially male nature of a man with Muto magic? Again, notice that none of the spells that do this sort of thing even say they'll change the gender, just adjust things for an apparent change of gender.
The fire created by igniting something with magical fire is not magical. If you use a Pilum of Fire to ignite a forest, after the "Momentary" duration, the forest in fire is not magical, not resisted by MR and progress naturally.
Therefore, you cannot use Corpus to act on a natural fire created as consequence of a magically mutated-in-fire magus.
Sure, just like if you magically grow claws and cut someone with them, the cut cannot be healed with PeAn, for example. But my question for you is why the magical fire can be affected by Corpus if the Muto magic has change the target so the target is no longer a person. Is it that that fire is actually still a person and can be affected by Corpus? (Yes.) Why? The essential nature is a person, and Hermetic magic cannot change that. It disguises the person-ness with fire, but the person-ness remains nonetheless.
Meanwhile, we have a statement that a man has an essential nature of male as well as a statement that a consequence of male essential nature is not getting pregnant. House rule them away if desired, but all three of those statements (those two plus Hermetic magic not changing essential nature) are canon.
