A power is a power is a power?

[FeiLin]

All the powers that consist of advantages with enhancements and limitations are interchangeable regardless if it’s psi or another form of supernatural ability, right? Given the relevant modifier (generally limitation) is replaced.

Or is there something deeper to the various books of psi, sorcery, divine favor, etc, beyond a thematic coherence?

[Kromm]

Yes and no. GURPS Powers fills a lot of pages with advice on modifiers that go with some power sources better than others. For instance:

Magical, -10% (Powers, p. 27) covers strictly "depends on mana to function" and "effects can be blocked or dispelled." In many settings, however, some (not all!) magical abilities require one or more of "Requires material components, -10%," "Requires gestures, -10%," or "Requires magic words, -10%" (Powers, p. 116). The answer to "Which ones?" varies by ability and by user, even within the same power. Other powers probably won't have any of those three modifiers.

Superscience, -10% covers only the "can be neutralized at the source" and "has effects that can be blocked or canceled" facets of its power. However, it nearly always occurs alongside gadget limitations (pp. B116-117), which likewise can vary by ability and user, and might not make sense glued onto, say Nature, -20% or Spirit, -25% in many settings. See Powers, p. 107.

So, when moving abilities between powers, you'll have to be on the lookout for a lot of adjustments suggested but not strictly prescribed by the power modifiers – often on a case-by-case basis.

Still in the "in many settings" department, really meaning "in some campaigns," there's the unrelated issues of which advantages can form abilities for what powers. Powers also fills a lot of pages with advice on advantages that go with some power sources better than others. The most extreme are those that implicitly exist for only certain classes of powers; e.g., it's hard to imagine Spirit Empathy with Biological, -10%, or Digital Mind with Nature, -20% in most games.

This gets especially complicated when a setting prescribes that an advantage always occurs with modifiers A, B, and C alongside, say, Magical but X, Y, and Z alongside, for instance, Psionic.

And there are also cases where two totally different advantages are used to represent similar concepts for different powers. If the GM wants Special Rapport for magic but Mindlink for psionics, or Penetrating Vision for supers but Para-Radar with Penetrating for robots, or Infravision for elemental fire powers but Vibration Sense for elemental air and water powers, you just kind of have to know.

[Emerikol]

Also, a GM for a given setting will usually limit what is available to some subset. I can't imagine running a campaign where everything is available. Maybe a many parallel worlds type campaign but not many.

This is why GURPS is often referenced as a toolkit for building your own game vs just a game that you as GM have to make few choices before you start.

[DangerousThing]

Sometimes there are rules for using powers in a certain way.

For example, using GURPS Psionics Powers describes rules for using these powers. For examples, rules for groups of psionic individuals combining their strength and rules for using Extra Effort.

[Plane]

Originally Posted by Kromm

Magical, -10% (Powers, p. 27) covers strictly "depends on mana to function" and "effects can be blocked or dispelled."

what about "FP Cost and Source" on Powers 178?

[Anaraxes]

Lots of good advice above about aspects to think about. Small differences between powers can add more flavor to them, and GMs will often add limits or requirements to get the feel that they want a Power to have.

But yes, purely generically mechanically speaking just about any ability can be switched to a different Source / Power by changing out the PM if you're otherwise happy with the build and connotations that ability brings along with it. There aren't any lists of particular Advantages that are required or forbidden to be used as building blocks in particular Sources / Powers. In fact, I think one reason Powers builds most of its sample Power Modifiers to come out to the same -10% not because it's required as a rule that all PMs be -10% (a PM can be any value, and there are several counterexamples), but simply to make the long list of sample abilities interchangeable without a lot of recalculation. If a given ability makes sense to you as being powered by some other source and fits into your concept of a Power, then just copy the ability build, call it "magic" or "psi" or "ki" or whatever, and move on.

Worked examples like Psi Powers and Sorcery usually have a few rules tweaks to help make that system fit the vision of its author. Feel free to do the same.

[FeiLin]

Originally Posted by Kromm

So, when moving abilities between powers, you'll have to be on the lookout for a lot of adjustments suggested but not strictly prescribed by the power modifiers – often on a case-by-case basis.

Powers also fills a lot of pages with advice on advantages that go with some power sources better than others. The most extreme are those that implicitly exist for only certain classes of powers; e.g., it's hard to imagine Spirit Empathy with Biological, -10%, or Digital Mind with Nature, -20% in most games.

And there are also cases where two totally different advantages are used to represent similar concepts for different powers. If the GM wants Special Rapport for magic but Mindlink for psionics, or Penetrating Vision for supers but Para-Radar with Penetrating for robots, or Infravision for elemental fire powers but Vibration Sense for elemental air and water powers, you just kind of have to know.

That’s interesting. The answer to “what can be done?” is “anything!” whereas the answer to “why should it be done?” is “to craft the desired game”, and most of the considerations fall under the second category.

For us, in practice, it’s good to have some inspiration and crossbreeding (especially for the more thematically opened power), and the “soft considerations” come naturally

Originally Posted by Anaraxes

In fact, I think one reason Powers builds most of its sample Power Modifiers to come out to the same -10% not because it's required as a rule that all PMs be -10% (a PM can be any value, and there are several counterexamples), but simply to make the long list of sample abilities interchangeable without a lot of recalculation.

Yes, that’s at least partially what started the train of thought.

Originally Posted by Emerikol

Also, a GM for a given setting will usually limit what is available to some subset. I can't imagine running a campaign where everything is available. Maybe a many parallel worlds type campaign but not many.

DF probably come closest (in theory, at least), with all the releases, but in practice would need motivated players and GM (and probably at least one player power power, which would bring other practical difficulties).