Powers: Origins: Magic Powers
Magic Powers
Most GURPS campaigns focusing on magic will probably not use the Powers rules; rather, they will employ the "spells" system from Chapter 5 of the Basic Set and GURPS Magic. However, in some cases, usually in superhero or lightweight fantasy stories, wizards can employ powers without apparently learning and casting specific spells. These characters may have internalized the principles of magic so completely that they can improvise new effects at whim, they may be using gifts granted by magic-manipulating deities, or they may have been enchanted like a living magic item.
Unified Metaphysical Theories
In some settings, there may be no fundamental distinction between "magical" and "spirit" or even "divine" powers; "magicians" work by commanding or petitioning supernatural beings. Similarly, a world's gods may be exceptionally powerful spirits (certainly, some beliefs make little distinction between the two categories), or creatures of great magical power – far beyond any human wizard, perhaps, but not actually different in kind. Likewise, the gods, or friendly spirits, may grant their priests or servants useful abilities – which may in fact be "spells." A wizard might gain the ability to fly or hurl lightning bolts after years of study, while a priest might have the same knowledge and skill placed in his brain as a reward for his prayers, but they could still end up employing the same methods to exploit the laws of the universe in the same way.
Of course, whether or not the various power-users know that they are manipulating the same basic forces is another question. If there's a rivalry between "toadying priests" and "atheistic wizards," they might both become angry at anyone who points out the truth. Certainly, gods with any pride will object to being placed in the same category as mere human conjurers.
Giving apparently different powers the same origin and fundamental nature has various practical advantages for the GM. It can make interactions between different power-users easier to manage, for example. However, it may also make the setting feel less rich and complex.
Magical Psi
In some settings, "magic" and "psi" both tap the same energies, in one case by study and formal disciplines, in the other by raw talent and willpower. If magic is simply psi power unlocked by self-hypnosis, the way that magical powers are defined for game purposes should reflect this.
"Pseudo-magical psi" might be stopped or negated by anti-psi powers (-5%) and have a minor Accessibility limitation to reflect the need to perform brief incantations, make small "casting" gestures, and have "spell components" to hand (-10%) for a net power modifier of -15%. (This assumes a low-tech generic fantasy setting where psionic technology doesn't exist, or at least can't produce effective countermeasures.) On the other hand, if psi can achieve almost anything, but most humans need lots of complicated procedures and tools to produce even restricted effects, it may be simplest to treat it as magic. Psi might even use the standard GURPS spell system. ("Mana levels" would probably not vary much in such a setting, although some areas might be more "psi-friendly" than others.) The most important practical effect is that "magic" and "psi" could always interact directly, able to detect, negate, and even enhance each other.
Cosmic Magic
Likewise, magic and psi may be "cosmic" in nature, manipulating reality directly – though only the most powerful adepts comprehend its true nature and potential. Magic and full-blown cosmic powers may interact, and magicians might shed most of the restrictions on their powers as they advance in the art.