If you do not put any experience points into a Form or Techinque, that Form or Technique is at 0 - all apprentices are taught all Forms and Techniques to that level to start with - its called "Opening the Arts". So '0' does not mean 'total lack of knowledge' here.
Does this mean that I can cast spells that require Form or Technique (or both?) (or a requisite) that I have at level 0.
So if I have Creo at 0 and Ignem at 10, and Int of +3 and Sta +3, and Magic Theory 3 - I can learn Creo Ignem spells up to the level:
Magic Theory +3
for a total of 19.
And even if I had Creo and Ignem at 0, I could learn any Creo Ignem spell up to level 9. (0+0+3+3+3 = 9)
I could even cast Spontaneous CrIg spells up to level (Creo 0 + Ignem 0 + Sta 3)/2 = 1.5 - rounded up to 2 - if I was willing to spend a fatigue level.
Am I missing anything? Is this how it is supposed to work?
Yes. If you have a Score of 0 in an Art, you are just not very good at it. You can still use it though. It is the Hermetic Opening of the Arts that gives you are Score of 0 in each of the Hermetic Arts.
Although I don't think it's an official rule, we also use a houserule about this. If a character rolls a 0 on the casting die, then there are an additional 3 botch die for each Art with 0 score that was involved in the casting total. This works quite well.
That seems kind of bizarre. Does anyone not spend the 6 or so xp to get 1s in the Arts you otherwise aren't interested in? If the difference between 0 and 1 is that big, you'd have to be insane not to, given how little cost in involved.
in character - the parens teaches a range of Arts at one time (not restricted to one subject) (and OOC splits the XP between them)
OOC - players usually have a modest number of XP left towards the end of chargen, and a major shortage at the beginning (for the big items - the Art score 10+).
When you have 12XP left, you can have 12L1 or 4L2 or 2*L3
Given the ease of increasing Arts given a season with a good book, I usually go for the 2*L3 and "specialise" a bit, to get better results initially... a String of Arts L1 is not actually much use...
Yes, in that campaign you must never generate a character with an Art score of 0.
Makes the rule silly in the end, as no-one will hit it...
ArM5 went out of its way to remove "no-one will hit it"rules, and some "only ever rarely" ... e.g. the "no more than 3 levels in a season" book study rule: in ArM5 you can exceed 3 levels in 1 season - but in practice, only for a Art starting at 0..3. After that it never happens again.
(You can't in practice manage it at all for Abilities - you need 30xp to get from 0..3 and just can't quite get that many!)
For normal skills, you can spend one XP to get the skill at 0 - at which point you can do it without extra botch dice you would get otherwise. Skills that cannot be used unskilled can be used if brought to 0.
So treating Art score of 0 as part of the spell acquisition and casting totals makes a great deal of sense - with no special treatment just because of the 0.
Well, it has been used in our campagin. It's not that big a deal. Largely, because you still have a really good chance of casting your effect without botching.
Say you have one of the Arts you are using for an effect at Score 0, and no other reason for botch die --- then you are rolling 4 botch die. Your chance of botching an effect (rolling a zero on the casting die, and at least 1 zero on the botch die) is only about 3.4%. Whereas, if you weren't using this rule the chance of a botch would be 1%. It doesn't seem like a big worry to me.
It also only really effects specialists casting effects in the areas they are not specialised in, so it doesn't come up that often anyway. But when it does, it makes things a bit more exciting. YMMV.
You forgot the big one. Sumae. If a sumae is available and the character will study up to the book max level one or two are just waiseted experience points.
If a character with art 2 studies from a level 5 quality 15 summa for a season they end with art 5. If a character with art level 0 studies for the same season they still end up with that same art level 5.