[RogerBW]

A concept which I think John introduced me to which is still important in 4e is the "Mage Number": IQ + Magery - 2, or "the skill level I will get by spending one point in a normal spell". Given that anyone with more than trivial core-rules magic will have lots of spells, it's important to keep that number in mind when designing the character.

The default maximum Magery was 3 for many years, but that isn't the case by default in 4e, and Artillery Spells has some with M4 or M5 as a prerequisite.

I seem to remember Armin commenting that "Magery 0" had to be introduced as a whole separate advantage in GCA because everything else could work on the basis that a level-zero advantage would cost zero points. It does seem a bit odd, and it would be nice to have it broken out as a separate thing (a Detect, in effect) rather than being a prerequisite for or side effect of big power.