Definition of 'Active' and 'Passive' use of Ablilities

[Nedorus]

In another thread (concerning Walls and Power Parries) the point came up, that

the character actively using their powers; the idea for Walls doing it seems more passive

In trying to understand this I came across:

Originally Posted by P168 DEFENDING WITH POWERS

Power Block counts as an active use of the defending ability, even if that ability is normally passive.

Now I'm wondering what exactly constitutes an "active use" and a "passive use"? and where I would find the "definition".

I'm roughly aware that some abilities (like Detect) need some maneuver or concentration to be used and others (like Danger Sense) do NOT require this. So the former might be classified as "active" the later as "passive".

However the above quote from Powers seems to suggest that there is a more formal definition. Or is there?

[zoncxs]

"Barrier"
Damage Resistance N (Force field, +20%; PM, -10%) [Nx5.5]

This provides DR = N passively. You can attempt a power block, which is an active use of the ability, to provide 2xN DR. If you fail the power block, you get no protection.

A passive ability is one that does not need an "action" to use.

[Nedorus]

Maybe I mis-explöained what I'm asking.
My question is not about "Defending with Powers" but much more general. The quote from defending with Powers (Power Parry) were just examples to show where the question arose from and to set the general context of "active" vs. "passive".

So let me rephrase:

So given any ability, how could I tell that it is "active" or "passive"? What modifiers would change that?

e.g. "Always On" abilities are "passive" all others are "active" or something like that...

[zoncxs]

Its less about "what modifiers" and more about the description.

An "active" ability requires a roll or action to use every time.

Example:

Innate attacks are active abilities because you must choose to use it.

Damage Resistance is a passive ability because you do not need to choose to use it.


Modifiers are capable of altering this.

Example:

Putting Active Defense modifier on Damage resistance makes it into an active ability that requires a skill roll to use.

Putting "Cost FP" on enhanced move makes it an active ability to use (because once you stop paying it turns off).

The description for the ability should tell you if it is active, and what you must do to activate it, or if it is passive.

[Nedorus]

So contrary to my assumption, there isn't a "formal definition" of "active" / "passive"?

So what about my original example of "Danger Sense". It requires a roll every time it's used...

Is it active or passive? I thought it was passive, but taking what you said it seems "active"...

I'm confused (@_@)

[Celjabba]

The definitions are in Gurps Powers, p153.

In short :

• A passive ability has effects that apply constantly, or that activate without the owner’s input in a specific situation.
  
• An active ability does nothing until the wielder takes a maneuver to use it or chooses to make a die roll.

Unmodifed Danger sense is passive.

Modifiers can change whether an ability is active or passive.
An ability may have both an active and passive aspects, see Powers for details.

Edit : added a missing half of a sentence, thanks Donny Brook